Philosophers often get a bad wrap, not entirely without justification. The common complaint is something like "come on, do we really need to analyze this thing in so much detail? Can't we just get on with life since the world keeps working whether we understand it or not?"
Without digging too deep into all the reasons why some people like philosophy and others don't, I want to use this opening example to talk about two purposes that often cross: pragmatism and completeness.
When our purpose is pragmatism, we care about getting something else done. That is, pragmatism doesn't exist on its own, it's in the service of another purpose. If I'm hungry, perhaps all I care about is eating, not the details of digestion or food preparation. I can be pragmatic about eating and be content with my understanding that if I eat a sandwich my hunger goes away.
The purpose of completeness can stand on its own. It can manifest as a desire to know everything and be capable of doing anything. We need not be about something to engage in completeness; we can engage with completeness itself and let it lead us to the places where our understanding or abilities are not yet complete. It creates a kind of unbounded curiosity to know more that can only be satisfied by total understanding of everything.
In the imaginary space of understanding, pragmatism and completeness act like dimensions along which our desire for understanding can reside. We might seek highly pragmatic understanding that is so incomplete it's opaque, we might desire completeness even at the cost of being pragmatic enough for our knowledge to be useful, and more often we find some path between them that balances our need to use knowledge with our desire to build it.
To return to philosophy, pragmatism and completeness show up as cross purposes both within philosophy and in the meta question about how useful philosophy is.
For any philosophical question, there is a pragmatic stance that says for some purpose we need understand no more. This is the kind of stance taken, for example, by Eliezer in "The Simple Truth" with regards to epistemology. In contrast, I've previously talked about what happens if you keep digging: you run up against the Problem of the Criterion and discover an epistemological gap that demands a leap of faith to cross (perhaps in a pragmatic way!). And so we see a tradeoff, albeit one with some hard limits, between pragmatic and complete understanding.
And on the question of the usefulness of philosophy, we find the same tradeoff. For some, what they care about is doing things, so philosophy may not seem so interesting because it's not helping them answer the questions that will help them do what they want to do. For others, what they care about is constructing an ontology that covers the world, and so they are not content to leave any corner unexamined. Neither is necessarily better or worse, just serving different purposes, and so better or worse depending on what we each care about.
Which brings me around to why I've bothered to examine the way pragmatism and completeness interact. In many discussions I think people end up at loggerheads because they want to make different tradeoffs between pragmatism and completeness, and if it feels like we're already at the Pareto frontier of pragmatism and completeness in a discussion, then that tradeoff becomes a fight. This is a problem that seems unlikely to yield to typical consensus techniques because it's a level up beyond and behind the object level discussion and may be invisible to the interlocutors. But, now that I've written a post pointing it out, maybe it need not be, and we can notice when our disagreements come, at least in this case, from trying to serve different purposes.
One thing this leaves out is how pragmatism contains the risk that you are completely misunderstanding what is going on. Sometimes the risk is worth it, other times it isn't, although it is hard to tell in advance.
Lossless compression scales arbitrarily. Lossy compression requires metadata about domain within which the compression remains valid.
When first attempting to solve my problems, I tend to favour completeness, playing out repercussions, considering possible paths.
It is only when I flip the switch to pragmatic, focusing not on fully understanding the problem, but instead on mostly understanding the problem, that I actually solve my problems.