I've seen this happen mostly at benefits. It's either the old fella who plays and sings fine except when drunk, which is usually, when he always goes overtime, or more often it's the auction, held in the middle of the sets, where the MC/auctioneer decides to auction stuff off one pie at a time instead of doing them in pairs or whatever works, or he decides to spend far too much time being funny. Then the second half performers have to rush and reduce their sets, and still it runs overtime.

I've also seen MCs, having made performers wait forever, not bother in time to send someone looking for the next performer, who's nipped downstairs for a beer thinking he's going to have to wait another half hour.