Easy 10
Brain dead MUG SHEEP
Problem is you can't get the 3 points back on Monday morning. With the colossal amounts of money at stake, especially in the PL, clubs can't afford to be shafted by poor decision making. I'm not advocating a review of every decision, but certainly penalty decisions and handballs could be reviewed given the impact they have on a game (and potentially a season).
You're never going to have a "perfect" system though. You only have to look at the disagreements between pundits and fans on some penalty decisions to know that going to a video review to make the decision simply opens up a whole Pandoras Box of new issues. Its NOT always blatant, and its NOT always black and white. If a ref makes a call off the back of a video review, you'll inevitably STILL have plenty of fans, managers and pundits disagreeing with it - except this time its worse, because he's had time to look at it again and (maybe) still arrived at what some will interpret as the wrong decision.
You can't always rely on a correct decison, all you can ask for is an honest one. Video reviews for fouls / offsides / handballs would resolve nothing. It'd just make a whole NEW raft of controversies.