standing in the horse stance or any other stance teaches you to root.If you have a poor root say in a horse stance then when you move your horse is not going to be any better,so first you have to learn how to root in a non moveable stance first then move on to rooting while moving.In Wing Chun,the style I practice the first form does not move.Its because if your root is no good why bother to move on to the second level which teaches a movable root and other things..