Cracking up at what Warwick Slade said! YESS! Love it!
Singing in an informal singaround is singing a song, not "a performance" to my mind anyway. As I said higher up the thread, too many people talking about and confusing entirely different scenarios here. If I get invited to do a floor spot at our local folk club, yes, I will try to get up there on stage, with a mike, and lights burning my eyeballs out and sing a song i know from memory. Then I'm performing.
But next week, with the same people, down at the pub session, if I want to sing something I know pretty well, but haven't yet fully memorised completely, I might put the words in front of me and glance at them when needed: that's participating, not performing.
And for other sessions now, I don't take big folders: just pick 2 or 3 song-sheets which I might never use, because, as others have said, you might change your mind about what's the best song to sing next, according to what's gone before.
I' also getting on a bit and recognise that there are still things in the memory bank that I learned at school or in my late teens, but trying to learn new songs now, becomes increasingly difficult. I have a far better memory for tunes than I do for words: that's just a facet of how my brain works, and you who can learn song lyrics after reading them through twice are surely blessed: but DON'T try to tell everyone they can do the same, because we are NOT all made the same way.