I think most people rake the poo out maybe on a more regular basis than deep litter. I'm guessing sand isn't quite as absorbant as pine and straw. I considered a sand box under my roost to be able to just rake the poo out...not sure yet as everything in my coop, run, chicken plans are in a state of constant rethinking and reworking. Nothing so far is permanent! hahahah. I think thats part of the enjoyment - just messing about with the little fuzz butts
Sand in a run probably works good if you have some muddy issues, I would think it allows the water to drain thru in a rain, and if its deep enough...
just guessing until someone more experienced chimes in...
interesting tho, never thought of sand as deep litter but the more i ponder it and the more i see how poo breaks down, it seems more plausible.