re classical performers: I think it is fair to say that most folk music is rather simpler. Usually shorter, too, though it may not always feel that way.

My wife sings from memory. She feels it wouldn't be right any other way - that it would be being impolite to the audience. (I am reminded of the treatment of mime artists in Pratchett's Ankh-Morporka. Hung upside down in a viper pit with the mesage "Learn the words".) She can be quite entertaining on how non-folkies in her choir sessions first react to being expected to sing without their dots.