That's a good question, but it doesn't have a very satisfying answer. The "point system" doesn't actually do anything practical. It is a way for frequent contributors to the site to be recognized for their contribution and also is a way to compare contributors based on how much they have added to the site's content. Aside from bringing out a little healthy competition, and giving users a chance to see who the most active question answerers are, the points can't be "used" for anything.
By the way, welcome to eNotes! I hope you enjoy your experience on the site and be sure to ask any more questions you might have!