If you don't drill the handlebar, or remove the little 'nub' as you call it, tightening the grip assembly down can cause a bind or worse, a crack in the plastic. The 'nub' is there to prevent the grip from rotating on the bar. Most drill a hole to keep things from moving but I've read a few posts from guys who have had luck just tightening the grip after removing that tedious 'nub. Personally, I drill a 5/32 hole in the handlebar.
Tom