powerlifters do this because in competition they care a lot about leaning back at the end
I have never done this I just push through the legs untill i'm perfectly upright, leaning back at that point is crazy but a requirement for powerlifting competition?
I don't compete anyway
I know, they do it to prove they've locked out.
But that is totally exaggerated.
As a matter of fact, I remember not too many days ago lurking at starting strength and a guy posts his form video asking why his back hurts so much on the deadlift, when he only lifts 135.
Guess what he was doing wrong and what the coach told him to stop doing.