I was told that the reason that a steep descending turn is taught these days (I think it wasn't when I first did my PPL?) is so that you can get down through a hole in the clouds, having stupidly and illegally got yourself stuck on top of them.
Steep level, climbing and descending turns do not come within the range of normal flight procedures and the practice of these manoeuvres serves to improve co-ordination and enhance the pilots ability to handle the aircraft in unusual situations such as the one quoted above, collision avoidance and others such as engine fire in the air...
Another useful practice manoeuvre an instructor can teach is the steep descending turn
with flap lowered to simulate a situation where the pilot is inadvertently operating at steep bank angles during the final stages of a spiral type descent whilst positioning for final approach during an actual forced landing without power and/or fire.
VFE.