I feel more secure singing if I have the song memorized. I'm not a fan of people who think that its easy to sing folk music and then fumble through connecting chords, words and tune together because they didn't bother praticing. Cheat sheets are fine by me; since I'm working now in a duo we need to write down more about our arrangements and I check for that rather than words usually. But I figure if you know the song but need the memory aid, partly for confidence, and it means you sing better, use it. People chuck jokes at me for closing my eyes while I sing, so does Eric Bogle.