I always sing and play from memory, as much a courtesy to the audience as anything. I don't understand how anyone can play for dancing from the notes. Watching the dancers feet is as much an aid to the band and you see some amazing and amusing sights on the dancefloor. A transparent backlit dress on a lovely dancer I would have missed if I was playing from the notes. And if you lose your place during a long song a phrase regarding a canoe and no paddle comes to mind.