Anybody in SE La had sand pumped under their slab?

Plumber had to bust through my slab and I saw there is a good 2 feet or more of settlement under there. A huge gap. I know possums and other critter live under there.

House is on pilings so slab is stable. What’s the purpose of pumping sand under the house? I heard that the added weight can cause damage to underground pipes, but I have no idea. Seems like a lot of money and I am not even sure it is necessary. (I grew up in a place where the ground didn’t sink. My dad thinks the sinking is the equivalent of a natural disaster.)