One must be a bit considerate of one's audience, and of the organisers of the session. At the Crofters club in Cambridge, anyone called up was normally expected to sing two songs. But I once sang a full version of Rosie Anderson, a beautiful song IMO, but loooong. So I just sang that one and then ceded to the next singer. The song went down very well, and the organisers thanked me for having ceased after it and not over-hogged attention by insisting on my full quota.

~M~