Nothing, that was one of the main problems, it would mean the end of small developers who can´t afford to pay such a big amount of money in case a free game blows up. Every install would count (it will in the new version of Unity) and by every install they really mean it, no real protection against piracy and I think they were trying to see what would happen in case someone installed the game multiple times out of malice. There´s a lot of interesting and messed up details about that plan