Personally I feel that I can either communicate with an audience or with a songsheet and I have chosen the former. This may lead to occasional lurches in the lyrics but so be it. Mike and I spend a lot of time becoming familiar with a song (sometimes months) before we give it its first outing. Also, its first outing may well be its last!
Everyone makes their own choice.
What really ticks me off is those people who have to perform a song the day after they first hear it (I don't understand how they can) and those who still make mistakes with the crib sheet in front of them. (Oh, and those who haven't bothered to learn the tune either!)I'll stop there.