I much prefer open sessions in a bar to playing in folk clubs. Nothing wrong with folk clubs, by the way, and I've spent many happy hours in them, but I just prefer the spontaneity and communal music making in a session. I know what you mean about the relaxing nature of a good session.

I think that responding to a request - in whatever way is appropriate at the time - is always a lesson in dealing with people and adds to one's store of knowledge as a performer. "Toughens" is perhaps a slightly extreme word to use! :-)