When diving, your wing needs only enough lift to compensate for the weight of your breathing gas plus the compression of your exposure suit at depth. Those using suits which don't compress much, such as dive skins or drysuits made of trilaminate or crushed neoprene, will also want some extra lift in order to be able to float comfortably on the surface. And of course the whole rig needs to float by itself if you doff it at the surface.