It probably just fixes some amazingly fun exploit they found after they sent the game off to the factory.

What exactly does patches do for the game?

Patches fix bugs in the game.

Specifically patches store information that is used to change the game's data files in a way that updates the game to the latest version. This way by only saving what has to change you don't have to download the entire program over again to implement those changes. Patchers that just outright download the whole file over again are getting more common though I think lately.