The debate on whether to leg yield or not is not a new one. Certainly Classical Dressage purists sit firmly on the side of the fence that says leg yield has no benefits to the scale of training whatsoever and may even hinder progress.
So how you do reconcile this when the movement is asked for in tests? I do not know the answer to this question. It is a matter for you to consider when you examine the horses ability to progress beyond training/elementary level.
The primary benefit of leg yield is to simply teach your horse to move forwards and sideways, however, the hind quarters do not take more weight and the horse finds it difficult to remain light in the forehand (often the act of leg yielding puts the horse onto the forehand!)
Shoulder-in, travers (or haunches in) and half-pass are far superior exercises to the leg yield because all three of these exercises ensure that the horse’s centre of gravity is placed directly in the path of the activated hind leg.
Riders at all levels should seek to become skilled at these exercises due to the fact that, done well, they significantly benefit the horse’s gymnastic ability.
Patricia – The Dressage Tipster