Lots of faults arise when the horse is drifting to the right or left of the fence because the driving force isn’t symmetrical from both hind legs. During the airborne phase, the horse get twisted and he has a tendency to land always on the same front leg, which with time, will bring some articular and tendinous lesions.
The goal of this exercise is to get the rider and the horse to stay perfectly straight relative to the middle of the fence and on the jump itself.