I've found different venues and groups of people take on their own style, basically bonding as a group according to the pace of the venue.
I have sessions at my place regularly. It's round the room and everyone gets heard, unless they just want to join in in the background. It's important to have someone keeping an eye on who's next, because there's occasionally someone who tries to sing more than others.

when there are outstanding singers there, I try to make sure they don't do too many requests but get to do their own choices as well. otherwise the session can change from a musical sharing to an on-demand performance.