banjoman has it right:    "I would rather see someone make the effort and the odd mistake" than rely on written words in front of them.

I'm with him all the way.    I have unlimited respect for someone who makes the effort without crib sheets--or especially books.   Reading off a crib sheet, or worse, out of a book--not so much respect, to put it mildly.    So it may not be perfect.   The fact he or she has tried means they have actually put some work into preparation--they care enough to do that.   Any performer, even of one song, owes that to the audience.

I don't even mind if the performer has the sheet in hand while singing. But use it as a talisman---don't look at it.

Yes, there may be songs and performances which are worth hearing even out of a book (and only a book compiled by the singer)--particularly long humorous songs    But this situation is the exception that proves the rule.

It's rare, to say the least.