Why would an inch difference either way make a difference when doing bench press?
if someone is using the safety bars in a rack that has 2" spacing one setting could be too low and the next one up too high so having blocks to adjust the height of the bench will give the lifter a proper range of motion without worry of getting pinned by the bar.
We don't know what our limits are, so to start something with the idea of being limited actually ends up limiting us.
Ellen Langer