Imperfection is what makes music good, and human. It's the reason why drum machines never got that popular when they came around. They were just, too perfect.
A mistake happened to me just now. I was writing this thing in F#-minor and I accidentally skipped a note. And it sounded a lot better with that note missing. This was on paper though.
EDIT: Sorry, I didn't see there was a page 2, so I didn't notice the "new" discussion about playback.