There's a misconception that therapy is like paying someone to be your friend. While most therapists would disagree with that statement, there is a kernel of truth; therapy can often focus on emotional support, and getting those needs met. I sometimes joke that when friends need help, we suggest they see a therapist, yet in therapy, clients are asked to vent to their friends. This may sound like the person is being tossed back and forth, but there are two things at play here. The first is that many people rely on a few friends for more support than they can handle (hence being referred to a therapist), while others see a therapist partly from the worry of overburdening their friends (hence being challenged to open up to friends). The second, more complicated piece is that therapy and emotional support are actually two different things, fulfilling different needs, and there are many cases where one would work far better than the other.
The first and most obvious difference is that therapy is one-sided. The extent of this differs on an individual basis; some therapists may reveal that they too have had a parent pass away, so the client feels understood, while others may never mention their kids or partner under any circumstances. Emotional support, on the other hand, can go both ways. When a friend vents to you about their family, you can share similar experiences in greater detail, whether to tell them you can relate, give them advice, or even just to vent yourself. We are social creatures, so this can help us forge a deeper type of connection.
Ideally, therapists are unbiased, and non judgmental. Of course, this is difficult in practice, which is why many therapists see their own therapists. Being in therapy can help therapists separate our own past experiences from the client's present, and compartmentalize anything that comes up without just shoving it into a messy closet to be dealt with in the far future. In contrast, your friends are likely to have biases, whether they're aware of them or not. Even a friend who wants the best for you may have a particular idea of what that looks like, whether that's in judging a potential partner or convincing you not to apply to college far away so you don't move. Friends also have little to no incentive to work on this, since this comes from having a deeper connection and wanting to stay in each other's lives. At best, a friend may be upfront about their judgments, letting you know that they struggled in the subject you want to study, and thus might not show enough excitement about it. This can in some ways even be helpful, particular if the thoughts and feelings of your friends matter a lot to you. However, if you want to make a decision without worrying about being swayed by the influence of others, you may want someone more removed.
A therapist is going to provide a particular kind of expertise, though this is going to vary widely. A therapist's expertise depends on training and experience, and their focus can be anywhere from particular age groups or phases of life to types of diagnoses or lifestyles. This means whatever they specialize in, they know a lot about, including what's typical for people in this category and what problems often come up. A therapist who specializes in trauma is going to have a good understanding of how triggers work, and one who sees a lot of teenagers is going to understand the norms and culture of their generation. A good therapist will also provide disclaimers around any areas outside their scope or experience. For example, a therapist won't be able to give you medical or legal advice, but could help you deal with the stressors of finding a lawyer or help you examine your guilt around food. Of course, not everyone needs a therapist who specializes in their issue. Most therapists will know how to handle something like work stress or post-breakup depression, since these are pretty common issues. In some cases, you may need to find a therapist who understands you for your personality or lifestyle, like someone who understands your culture, is trained in trans issues or who has worked with military families. It all depends on your issues, how they show up, and how much you bring yourself in.
To contrast, emotional support from a friend can be within and outside your friend's expertise, but their knowledge is limited to their experience. You may have a friend who is a nurse who you ask for medical advice, or a really tech-savvy friend to help set up your printer. Unlike a therapist, your friend is not confined to their expertise. Your college friend's advice to try a particular diet could come from a deep understanding of nutrition and health, or from a single article they read. However, this knowledge and expertise includes knowing you and your history. A therapist knows as much about you as you tell them, but a friend may have seen you dump your ex and regret it, and know that you're likely to do this again with your current partner. A childhood friend may even have met your parents and know that you get your anxiety from your mother, or that your father's strict nature has made you afraid of failure. Of course, such insights may or may not be correct; emotional support is usually higher variance.
Aside from support, therapists teach clients social and emotional skills and techniques, provide access to resources, and help clients process difficult life events. A friend can help with some of this, but not all. For example, a friend can recommend a psychiatrist or help you find one, while a therapist can talk with your psychiatrist so that each knows how to better help you. A friend can help soothe your emotions and talk things through with you until you feel better, while in therapy, you can have an ongoing conversation that analyzes and processes anything that comes up around these stressors after the feelings seem to have faded. In some cases, this processing is the best way to make things better. However, for some, it just helps to have someone who cares about you around. A therapist may be able to talk with your doctor about your case, but cannot give you a ride to and from the clinic, or treat you to lunch after your appointment. Friends can provide comfort in daily life in a way that a therapist cannot.
Good therapy is supportive and collaborative by design. Client and therapist share goals, and everything is confidential. Confidentiality can differ from person to person in friendships; you can probably think of a friend or two who can't keep secrets. Most friends also aren't thinking about your goals when providing support, though a very good or close friend might. Most importantly, when you lean on your therapist, you can know that they signed up for this. In fact, this is another reason why therapists often see therapists themselves; it's our way of taking care of ourselves, given that we sign up for a lot. Emotional support, meanwhile, is only one aspect of friendship, and not all friends will want to provide the kind of support that you need. If you notice yourself relying strongly on friends for emotional support, that's a sign that you may need to see a therapist; otherwise, it can hurt your relationships.
This isn't to say that you shouldn't get emotional support from friends. Part of the work in therapy is to learn to do this in a healthy way, whether you're leaning on others or you're supporting them. The best scenario is a good balance of give and take that doesn't leave one person drained or unsatisfied. Good therapy and a good emotional support networks are not competitors, but rather two great tastes that taste great together.