Running shoes allow for first cushioning (to some degree) then an aid to transfer the energy into a push. All runners are different, but in theory the better your bio mechanical efficiency is (including body weight) the less cushioning you would need. My opinion is, it is better to be able to feel what impacts your feet are dealing, so that you can adjust your running style to aid efficiency. Less cushioning seems to make more sense. Although in ultras where foot comfort is important, they may be useful. But they are not for me.