It looks horrible. I've always been taught to keep your back flat against the bench, I don't know if it helps in competition but for help in building strength in your chest I can't imagine doing that.
That helps to keep the tension on the pecs. Where a PL couldn't give a damn less about squeezing the pecs for hypertrophy but care more about flaring the lats and cutting our range of motion down it serves is quite well.It looks horrible. I've always been taught to keep your back flat against the bench, I don't know if it helps in competition but for help in building strength in your chest I can't imagine doing that.