You calling me daft? (we use Z for several effects)Simon said:(e.g. daft games that want to sample the Z buffer).
Kidding , but seriously, there's just so many cool things you can do using ZBuffer (particularly if you have some support for 24-32bit number arithmetic in the rasterizer). And it's hard to beat constant time usage for particular effects as opposed to alternative methods of doing it without postrender ops.