I have often been puzzled when somebody gets up and sings a song for which they obviously have to read the lyrics word by word, saying "I just heard this song for the first time yesterday, and I had to sing it...". I know sometimes when you are excited about a new song you can't wait to share it, but in most cases it would be better shared if you'd practiced it first. It's usually much better, when performing in public, to sing something you know well.