But in the context of therapy... the most "therapeutic" therapy I've had was when I've had something on my mind that I couldn't really talk about with others.

For example, some friend-related things I can only talk about with my spouse. Some spouse-related things I can only talk about with my friends.
But then there are occasional things I'm working out where I think I'd like to workshop them a bit before I bring them to an audience I actually care about (eg. something odd happened in relation to my father once that I couldn't speak about with others because they knew him, and it would embarrass him for them to know. I worked with a therapist for a while because I couldn't humiliate my father but I had to get these things off my chest)