Basically, it is to prove that the product is original and not pirated. 

The importers also need to pay for the sticker. I think it's RM0.20 per sticker. Theoretically, each sticker has a specific id that must match a reference number on a specific game disc. For example, sticker A001 must match game A001. If sticker A001 is stuck on game A002, then the authorities can send in their troops and rape and pillage the shop. Most of the time, they don't follow the regulations strictly. Only when someone files an official complaint and they have to do their "job".