Especially as your main account
Edit: I edited the question so that people also feel free to answer the opposite question
Especially as your main account
Edit: I edited the question so that people also feel free to answer the opposite question
My policy on this is inconsistent, because my opinion gradually changed.
Ten years ago, I didn't care about who sees my name, because from a larger perspective, I am a nobody. So I used my full name, because the articles I wrote (not in English) often impressed smart people, and it was nice to meet someone and say "Hi, I am Viliam", and the other person was like: "No way, that Viliam, the blogger? That's awesome!".
So it seemed like there are some advantages and no disadvantages; and I was also thinking that maybe in the future I could become more famous and perhaps have a large blog with ads, and maybe even sell some services online, in which case already having an audience would help.
These days, almost everything is the other way round. I have kids which keep me busy all the time, so my blogging frequency is maybe one article per year. The chances of doing something big online are practically zero.
I am still a nobody from a larger perspective, but once in a while I change a job, and I feel like there is an increasing chance people may google my name before the job interview. I don't need some idiot to freak out about something controversial (from the idiot's perspective) I wrote online. Not that I write anything bad (from my perspective), it's just... the set of things considered controversial is large and growing, and I have no idea what will be the hot topic of culture wars in 10 years when I will probably still need a job... and even strong self-censorship (which I am psychologically incapable of) would not necessarily save me, because people can also be guilty by association. I mean, just being on LW could already make me a monster in some people's eyes. (Now imagine ten years later, when the robots actually rise up and start murdering people, and the people will need a non-metallic scapegoat.)
Third reason, I don't like how everything is connected these days, and major websites require your real name. A few years ago I happened to piss off someone, who then started contacting my relatives on Facebook. (Note: This was unrelated to politics. I just happened to meet a crazy person.) If you use your real name, it's trivial to find your family, right? They are on Facebook, among your contacts, many of them have the same surname; and the more diligent ones even spell out their relationship to you, and tag you in their photos to make it more obvious. That was quite traumatising for me, and I disappeared from online life for a few years.
So, these days it's like all disadvantages and no advantages.
If I could travel back in time and advise my past self, I would tell the young aspie to make up a pseudonym (one that will not feel silly in ten years) and use it consistently. That has the advantage of building reputation, especially if I would use the pseudonym to introduce myself in real life outside of job. And a quick google by HR would not reveal anything. Yes, this has a possibility of being outed. But it is very difficult to keep perfect pseudonymity anyway. For example, if I started selling something online, I would have to reveal my legal identity to my customers. I don't need the level of Satoshi Nakamoto, but the level of Scott Alexander would be nice. (Well, that's what I think now. Who knows what I will think in ten years.)
Considering that these days I don't have time to blog significantly, this doesn't feel so urgent. I changed my name to "Viliam", which feels like a sufficient compromise for now. Maybe one day in future I will try to erase my past and start again with a new identity. (The things I wrote on LW will probably stay here; I would ask admins to silently update the username.) One trivial obstacle is that I don't have a pseudonym that would "feel right" enough that I would feel comfortable to use it for the rest of my life. (Fun fact: I actually had a pseudonym in mind that felt right; and then I met a person whose real name was almost exactly like it. Now the pseudonym feels lame, like I am trying to be him. So I need to think about a new one.)
I used to. When I returned after learning/deciding that the moderation policy was probably not as toxic as I thought, I stopped. TL;DR: "Man is least himself when he speaks in his own person. Give a man a mask, and he will tell you the truth." (EDIT: see also)
Reasons why the pseud was useful:
LessWrong was, and to a lesser degree still is, unfashionable, and my name is rare. Posts under my name are likely to be prominent Google results for my name, most relevantly for recruiters.
Being aggressive when a situation calls for it is scarier when your actions reflect irrevocably on you rather than on your pseudonymous reputation. A pseudonym can be abandoned, shedding any mistrust and grudges at the cost of also shedding any trust and friendships you had accrued; a real name cannot. (As an example of those coexisting, my primary Tumblr pseud is known to be blunt and confrontational, but this also gained me the trust to be invited to be a beta reader for someone's serial novel when the author wanted honest criticism. I could shed the former, at the cost of the latter.)
Multiple pseudonyms can be used in different places or for different purposes. For example, if I was Eliezer when he wrote the "letter from David Monroe" in 2016, and I was writing it on LW rather than FB, I might have created a new account DavidMonroe and posted it with that. A non-hypothetical example is that I have kept an ancient pseudonym active specifically for engaging in certain fandoms SJ loves to hate on, and less commonly for when I want to really let loose on someone I consider a bad actor. The 'right to be sued' is valuable but the ability to act outside it is, too.
(EDIT: When I wrote this comment my LW username was <FirstName><LastName>. For some of the reasons mentioned here, I have since gotten my account's name changed to <FragmentOfLastName> to make it less Googleable.)
I don't use a pseudonym, here or anywhere , but even though you're not asking I'll answer anyway to give some of the ideas that point in the other direction.
Overall, I feel like there are a lot more advantages to a unified identity than disadvantages, and using a single identity has gone pretty well for me.
I'm in multiple communities that are mostly separate but still have a lot of overlap. And people in that overlap are often the people I most want to talk to about intersections (ex: automating a piece of being a contra dance musician) If I used different identities for LW, EA, contra dance, tech, etc then I would miss out on these connections.
Actually successfully keeping your identity private is hard. It's especially hard because technological advance makes things retroactively and unpredictably no longer private. So I generally act as if I don't have privacy, and get the advantages of making things public.
I'm not very worried about this making things hard for me in employment, but I'm also pretty established in my career as an engineer at this point. I put all my side-project code on github, even things that I would absolutely not write in a work context. Though if I wanted to move into something EA-ish as my primary career, I think these years of public writing would really be very helpful.
In general I am really pro-transparency, to the point that things like "never associate anything with your real name unless it makes you look good and you can take it down later when the cultural tides change and that stops being true" are not at all a way I would like to live. If I do good things I want people to know that about me, but if I do bad things I want people to hold that against me. That keeps me honest. And history is really important: I have old blog posts that I definitely wouldn't write now, but the strongest I'll do is add a note at the top retracting them -- I would not try to hide something I'd written just because it turned out to reflect poorly on me.
cbr on reddit because this predates deciding to use my name or a simple variant of it everywhere. But I also don't use reddit much anymore.
When I made this account, that was just what you did as part of the online culture. You picked a cool username and built a persona around it.
Now it's just basic OpSec to never associate anything with your real name unless it makes you look good and you can take it down later when the cultural tides change and that stops being true. I have several pseudonyms, one or more for each online community I participate in. This makes it far harder for people to tie together bits of information that they could use against me.
I decided that handwriting analysis would eventually uncover pseudonyms, so I may as well use my real name and be continuously reminded that security via obscurity is falsely comforting.
I like having a bit of deniability and search obfuscation to governments and employers. It's not very strong information hiding - truth is entangled, and there's enough of a trail that anyone who tried could find me.
Using a handle/nickname/'nym/whatever is very comfortable for me - I've used this one (or variations, as the source got more popular and namespaces more crowded) for well over 3 decades, since before the Internet was around. I have friends from the early days who use my online name in person, because that's how they first knew me, and because my so-called "real" name is fairly common.
I live in a social environment where expressing opinions or otherwise giving information about myself could have negative consequences, ranging from mild inconvenience to serious discrimination. I have no intention to hide my real identity from those who know the account, but I do want to hide my account from those who know my real identity (and aren't close friends). I use this name for most online activity.
Names are a complicated thing. I have several, myself. I hardly ever use my birth/government name for anything except official documents. At work I'm mononymously known as Red for reasons so old they're forgotten to all but myself; but it's not so much a nickname anymore as it is my work persona; I even use it on the phone now. A very limited set of people call me Dad or Daddy. Almost everybody else calls me Kith, and that's the name I use online. It honestly wouldn't have occurred to me to use one of my other names here. I don't normally think of it as a pseudonym, but since it's not on my legal documents I suppose at least some people would.
My job is related to AI safety and I do not have employer's permission to discuss any details of my work. I do not intend to do it anyway, but being anonymous reduces the chances of something being misinterpreted, taking out of context, etc and causing trouble for me.
Even unrelated to my employment, my default policy is to be very careful about anything I say publicly under my real name - particularly if it has any chance to be seen as controversial (again, vary of repotational risks). Using an alias reduces the transaction cost of posting (still have to think twice sometimes, but do not have to policy my posts as hard).
I know a person who uses a self-taken name in real life. (Her given name is Anastasia, but she goes by Alice.) It doesn't have the advantages of online pseudos hiding someone's trail from unfavorable scrutiny, but it's important enough for her that she used to sign official papers with it and now has changed her documents accordingly. In her case, it's a matter of being her own self-invented person... and back when I used pseudo names online, it used to have the same aftertaste.
I prefer to be anonymous whenever there is not a reason to use my legal name. I see no benefit to using my legal name here.
I use my real first name on here. I'm trans, and developing as a rationalist was instrumental in realizing that, so the two things are kind of tied together and the name partly symbolizes the rational part of me. Also, I had a hard time thinking of a good username and didn't really like the idea of hiding behind one on here due to a variety of factors.
And I don't use my last name because I don't want this account tied to real life me. Real life me has to deal with normal people, whose idea of rationality is AI and emotionless robots. It's much easier to just quietly use rationalist techniques and frame things in normal terms than try to explain all that inferential distance.
For other sites, I use my full real name if I want the account to be discoverable (github/gitlab, linkedin). For games I use my first name where possible because it's one of the few areas where people use it a lot to refer to me and I really like being called Raven. My writing has a realistic pseudonym. And for everything else I use usernames.
Mostly my reason is what FactorialCode said - using your real name online was just Not Done for most of internet history. But also my real name is extremely generic and I don't like it or identify with it much.