I think that's a good question.
I've been reading trainers who feel the horse can already "do" everything, and that suppling exercises are, in fact, more for refining aids, and teaching submissiveness. It's interesting that a lot of these trainers ride Baroque horses. (Look for trainers stressing "lightness.") They feel that once you've got them completely submissive -- that is, listening and happy to oblige -- everything is possible.
But in my own experience, I feel the exercises do help expand the range of comfortable movement. To me, exercises like half-pass are just that, exercises for my horses, which they will definitely not do out in the pasture on their own! Note: I ride ordinary back-yard breeds.
Forgot to add: the flexing of the neck etc. can also go beyond submissive-training. I think it really helps my horses to know they can flex their necks this way and that, and not fall over, even with all that weight on them. Otherwise, they don't need neck-stretching exercises. THAT they do all the time while browsing.
Last edited by Beling; 02-22-2014 at 02:06 PM.