Granted you can sing the song with a cheat-sheet/music stand, but when you want to close your eyes, throw back your head and belt one out with feeling, you need to know the words/chords. Or if you like to establish eye-contact with your audience to sing a song, the stand gets in the way. However, if you're playing to an audience of blind people (as I have) then it doesn't really matter. All the best.
Seamus.