I've seen it done at open mics and such where it was obvious that if everyone was going to get a chance the one or two songs alotted to each performer would have to be of reasonable length. But there are those who, once they get in the spotlight, just don't want to give it up so they make sure they pick the longest song in their repertoire with plenty of long intrumental breaks. It's very annoying especially with the person running the evening's entertainment doesn't realize that they need to manage the evening and let performers who have run over their limit know it.