If you do it right, Nothing. If you do it wrong = lots.
Imagine if in that clip shown on ben, he did a 2sec pause, and no guy strapped to his back, and no safety bars. Then look at bens 3rd rep, the one where he looses control a touch and the bar twists (right side of bar moves forward, left side of bar moves backward). Lucky that spotter was there, or perhaps, the only time he pushes THAT hard is when he does have a spotter.
The point is, just be careful. Make sure, if things go pear shape (like that 3rd rep of bens) you have safety options in place where you dont get hurt. Powerlifters always seem to get hurt.
I personally prefer putting the bar down onto safety cage bars, wait a second or two then go up. Why keep all that weight on your spine for longer when its just a squat and squatting is not your sport.
If squatting is your sport, then different story.