they dont really "do" anything - they are made for bindings for skis that are generally over a 90 millimeter width in the waist. freeride bindings usually come with wide brakes or a wide brake option. if you have a ski that has a fat waist, then you most likely need widebrakes
but not in all cases
and you want them so your brakes arent too small, and so that the brakes will do a good job slowing down your skis when they dart down the hill at mach10