True my phrasing was not correct, but when the camera is on the floor, you look 'under ones nose', when the camera is near the ceiling, you look down on top of their hair, even when looking straight ahaed.
Cool tutorial, but it looks like it restricts all the camera action to the background, because the 3D effects are projected on the foreground.
If you try this while the character walks away from the camera to the elevator and from the elevator towards the camera, you'll have a hard time making it look real.
If al the action is in the background, and the used locations are simple enough, this can perfectly work.