What I like about singing unaccompanied is - well, the main thing I like about it is that it doesn't involve playing an instrument I can't play. But one of the other things I like about it is that you can't just get up and bash it out - without the guitar for safety-net, a poor performance sounds really poor. I've certainly heard far fewer ho-hum performances from unaccompanied singers than from guitarists - some are good, some are bad, but very few are mediocre.