There are some who can use crib sheets and give a great performance with the audience hardly noticing use of sheets if they are noticed at all. There are others who stick their nose into the paper and don't look or interact with the audience at all. Likewise I know some who use no crib sheets and give great consistent performances whilst there are others who don't use crib sheets and can hardly finish any song without fumbling to a halt half way through because they've forgotten the words. Surely the issue is not crib sheet or no crib sheet as much as being prepared enough to give the best performance you can? For many people being prepared will mean having a crib sheet to hand. If they give as good a rendition of the song as they can though where is the harm?

I agree the regular fumbling about because you haven't considered what you might sing that night, the not even knowing what key it should be in, and the making a noise during other people's songs are annoying.

There are occassions though where someone may, because of the way things have gone, choose to sing something they weren't expecting to be singing that night. That is often the way people share maybe less known songs.