I'm pretty sure that lifting your butt off the bench makes the lift a lot easier than keeping it in contact. I do it to unrack because it feels lighter and uses less energy. A lot (maybe most?) of powerlifters do it too, presumably for the same reason. It's also common to see butts coming off the bench when people struggle with the lift.
If you're doing the whole rep/set with your butt up, then you're effectively doing a semi-decline press, which is easier than a flat bench. That's why most people do it. That's why many people lift their butt when the rep gets hard, because you put your body in a way more advantageous position.
I'm pretty sure that lifting your butt off the bench makes the lift a lot easier than keeping it in contact. I do it to unrack because it feels lighter and uses less energy. A lot (maybe most?) of powerlifters do it too, presumably for the same reason. It's also common to see butts coming off the bench when people struggle with the lift.
If you're doing the whole rep/set with your butt up, then you're effectively doing a semi-decline press, which is easier than a flat bench. That's why most people do it. That's why many people lift their butt when the rep gets hard, because you put your body in a way more advantageous position.
oh wow, I completely overlooked this. I have not done a decline bench press in more than 20 years (because my gym doesn't have one).