The breather coming off of the cover vents excess gases and routes them to the bottom of the airbox. There the gases pass through a filter, the oil and moisture are caught in the filter, and the combustible gases are drawn back into the system to be burned w/ the fuel. I don't think it really affects performance whether you have it or not, but I believe it is an emission control measure in that model.
I ran mine without the tube and wound up getting an occasional dribble out of the cover, but not much. If you have the stock airbox then you could find a piece of breather tube to fit it, or if you're running pods and getting the dribble, put a hose on there and have it drain somewhere where it won't go under your rear tire or your pant leg. I'm not sure if it is wise to plug the hole, I figure it's there for a reason.
Welcome to the forum! Lot's of great folks here with plenty of experience.
-Tim
