This demo shows how a 3D object can be used as a mask (taking only its Z info into account, and rendering the background 2D sprite).

Ok,that's probably not the most interesting use of the 'Use Z Information' behavior... But think 'bluescreen' fx as used in movies, or games like 'Resident Evil': you can have real time 3D objects and characters within a prerendered background (2D sprite). To handle occlusion of the character in the scene, you just create a low poly version of the geometry of the scene, apply the 'ZBuffer only' attribute to this geometry, and attach the 'Use Z information' behavior to any object.