if you're going to compete in a PL meet than it matters but i don't think it's a big deal for just bb'ing or casual lifting, it can help give you a few more pounds on the bar and it's not a big deal the overload is still going on the upper body pushing muscles, i just saw a clip of Markus Ruhl's new video and he's doing barbell benches like that, lowering the bar slow and then exploding the bar up and his hips come off the bench a little bit, no big deal.