I used to use them, but then I just got sooo sick of the bed being a mess after one night because of DF tossing and turning and kicking the sheet out from under the mattress. It even starts to happen to the fitted sheet!
So now my flat sheets just sit in the cupboard..except for the one that's hanging off the doorway between the kitchen and the rest of the house, it gets put down in winter to keep the living areas a bit warmer..lol