I was referring the the old homes and practices that I saw while inspection for damage and repair after Katrina.
Because of the soil conditions, some homes with slabs on piling settled (6" more on one side than the other) and had gaping holes underneath. On one a boy said it was good the soil went down since crawling underneath the slab was easier than before Katrina when he went in to run new cable.
One thing about piers, is that they put a relatively concentrated load on a much smaller area and that is bad if the soil is not adequate. If one pier settles, that pier and adjacent floor can go down and the excess loads are transferred to adjacent piers.