IF you really want to see how much benefit you get from your legs, get an old bike inner tube, and cut a 400mm length from it, and tie it into a loop. When you swim next, use the loop to tie both of your ankles together, and then try swimming without any ankle movement at all, and you see how much of impact it has on your overall body position. Most people think they don't kick when swimming, they may not kick to get propulsion, but they will have a very little flutter kick that will aid their body position.