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The arch or the wide leg position?
Leg position is just whatever is best / most comfortable for the lifter to use leg drive to aid in the lift - trying to push yourself horizontally across the bench.Arch is a combination of creating more overall tension in the body, putting the shoulder in a safer position, and reducing range of motion.
There is an argument in powerlifting atm for changing the rules around benching, not so much because of the arch, but the combination of the arch and the grip width rule meaning people can do a huge arch, and a massively wide grip for their stature, and have almost no range of motion. If their grip width had to be relevant to their stature, rather than the same for everyone, we wouldn't see these 0 ROM benches.
I was watching powerlifting on Eurosport yesterday evening, wtaf is the bench press position about?
Some of the camera angles when the lifters were getting set looked like something out of one of those niche bars where the waitress fires a ping pong ball at you.