It needs the opportunity for a team to appeal for a review. To stop teams abusing it, they should get one go at it. If they lose the review that's it for that game. They could also be liable for yellow cards as a result of the review. So if Willian thinks he's been hard done to, Chelsea can make the appeal ASAP and it goes to the pitchside monitor. If Willian's got a case, they get a penalty and keep their appeal, if not, no penalty, no more appeals and a possible yellow for Willian. But it gives teams something to turn to if they think the refs are both wrong and will shut them up after the fact. Any complaints and the simple retort is "So why didn't you appeal it?" They'd just have to be pretty sure of their players.