Mary and some others have basically covered this topic.

In general the worst possible situation is a "Rise Up Singing" singaround--where there is absolutely no reasonable expectation that the singer will even have seen the song two from the bottom on page 34--but will insist on guessing on the tune and plowing through all 11 verses on the page.

We call the book "Sink Down Moaning".

Anything is better than that.

I certainly understand how people may forget words. But the solution (by Dick?) earlier--is the best--just make them up. Or skip to a verse you remember.

Most people would, I'd think, have a good idea of what they planned to sing--and could make sure they had it memorized in advance. If singing a ballad, it's more important to keep the story moving than to remember every word. And chorus songs--my preference by far--gives you a chance to remember the next verse.

Above all you want to bond with your audience--and it seems to me the best way to do that is to have them sing--a chorus or refrain-- with you. And the bonding will never happen if you are reading off a sheet--with no eye contact with your listeners--or worse, out of a book. Though I'll have to admit, if the song is good enough, even reading out of a book (except RUS) is not a disaster necessarily. There are very few songs or performers it is worth listening to who sing "folk" from a book or off a music stand--but they do exist.

And I would think it no problem for the performer in an informal, non-paid, gig, to hold the lyrics in the hand if necessary--just as a talisman. It would be good however not to look at them while singing.

Classical music, I agree, from singing in choruses for over 20 years, is vastly different--especially since the precision required is extreme--both in words and notes, and in such aspects as duration of note, cutoffs of words, dynamic variation, etc. Totally different kettle of fish.

I belonged to a madrigal group for about 15 years. That's probably between the two worlds. I pushed hard for the group to memorize pieces--and it was wonderful when we did.