Fair enough on the visibility point. I’m not sure that I agree on the rock thing though. If you are still underweighted at depth, to the point that you are grabbing rocks, you were really seriously underweighted to begin with, right? How did you get down in the first place? And why not just do a buoyancy check at the surface and adjust weight accordingly?
If you lose weights at depth, then you're underweighted and rocks come in real handy. Getting down while slightly underweighted isn't that difficult, but when I was a newish diver, ascending with an empty tank made it impossible to do a safety stop at 15 feet -- the DM had to hold me in place -- because I did my buoyancy check at the surface with a full tank. Now I prefer to be overweighted so I can quickly descend if there's boat traffic, and it keeps me steadier while doing U/W photography. Whatever the reason, I'd rather grab a rock than try to wrestle with positive buoyancy during the dive.