Here’s an interesting film clip of historical interest.This film made by Edison Laboratories in 1898 show a cavalry drill in which the troopers lay their horses down and then get them up again – without leaving the saddle.
The practical application for this maneuver falls into several categories:
To conceal the horse and rider from enemy observation or fire
To use the horse as cover to protect the trooper from enemy fire
To enable a wounded trooper to mount the horse
To recover from a stumble
Very few horses are trained to do this nowadays despite the maneuver still having some very useful purposes (such as trying to mount one’s horse in the field when one is injured).