I think the answer might depend on the person.

For me, it's not that my T stays back (I understand 'staying back' as not getting too involved, being respectful). I can give a few examples of what I feel is different from a friend:

- most people seem to have some kind of empathetic reaction when their friend is suffering. If the friend is depressed and tells them every day, or if the friend thinks about suicide, or is really anxious, they will kind of take on that feeling. They will feel with the friend, suffer with them and try to help make things better. However, that gets quickly exhausting. Imagine a friend who shows up on your doorstep twice a week just sobbing about their life, but never paying a whole lot of attention to you since they are so absorbed in feeling bad.
In this situation, I'd expect a T to of course have some empathy, but to be rational and collected enough to not just be depressed because I feel bad. I expect that I can go there every week, rant about the exact same thing as last week and I do not run the risk of losing the person I'm talking to. I think if you just rant to a friend once a week and don't do anything else with them, they will quickly abandon you.

- when I do start talking about difficult topics, I don't get judged or the topic gets avoided. Lets say abuse of some sort. For some reason most people avoid this topic if you start talking about it. They say 'oh, but it's not happening now' or they try to lead the conversation in a different direction. And that's often unhelpful, on the one hand because there's a need to talk about such things in a lot of people, and on the other hand because it makes the situation even worse. It also helps not to feel like a weirdo just because you did something that other people maybe do not do. It helps to feel normal.

- friends seem to keep the level of the conversation very shallow most of the time. Lets say I constantly am scared that all my friends are going to abandon me. I did communicate that for a while with them, and what I got back was 'I'm not going to leave' and similar answers. That's reassurance, which helps short term, but it doesn't solve the underlying problem. For some reason I'm constantly scared that people will abandon me. To solve that, I need to think about where that fear comes from. If I know the source then I can rationalize my feelings and that makes them less scary, intense and easier to control. But to get to the source I personally need somebody to guide me. It's hard to see connections in your own life sometimes, because you're so involved, you do not see the forest for the trees.