None of that is important in a session or a sing-around.

Oh, I wouldn't say that. In a folk club setting, whether I go along to do an unpaid floor spot or go as a paid headline act, the performance criteria are the same. And being 'professional' in an unpaid capacity - wherever you might be - is one form of entrée into paying gigs. You're seen at singarounds, and I've been given gigs from being at a pub session.