The advertised benefit is that if you throw away the cap and bottle separately, you have 2 pieces of trash to clean up instead of 1. The actual benefit is that bottling companies can charge more for a more complex mold, but the same amount of materials. Lobbyiest lobbied and tada! In reality both pieces end up in the same landfill or in the same water current to garbage island. Now we have an antiquated law and an annoying policy to follow.