Fair enough to only take one turn if the session is very crowded and it's a struggle to fit everyone in, but if there is plenty of time, then why on earth not? My friend and I also tend to choose rather different material from each other, we both sing, and we play different instruments, which can complement each other or how the song sounds. Plainly we'll have to agree to differ with some of you on this one.

Is there also "positive discrimination"? E.g.when so-and-so group, maybe slightly famous, wanders into a session, and immediately gets asked to sing, out of the usual run of things. Then "Oh well, there are four of you, so let's have 3 more songs"! It does happen: the performance is usually very enjoyable, but may mean that someone who has been patiently waiting for ages has to be left out. Now that IS stretching it a bit.