I think the special need is that the builder wants to make more money. Post tension is cheaper (less steel). It has been pretty much the standard around here (houston) for many years.

: : There could be another problem if you have a post-tension slab. You had better first locate the cables that run through the slab and make sure you don't cut or damage one. This can be done by x-ray, or you may be able to find the cable anchors around the perimeter "beam" of the slab. The cables run through the slab at right angles to the beam. The tension plates (anchors) are usually patched over with some sort of material that can be distinguished from the original concrete.

: : John