Most sessions I go to aren't total free-for-alls that just happened. Someone went to the trouble of getting the landlord onside; and someone (maybe the same someone) decides whether we're doing two songs each, or one song each, or 10 minutes each, or whatever; and someone (maybe the same someone) says "and now John/Jill's turn..."

And if someone has a three-song slot, and plays the same thing three times running, then someone else is likely to say "look, stop mucking about". No?

Graham.