Having a correct rider position is critical for building a solid relationship with your horse. When we are unbalanced on our horses back, they will become unbalanced as a result and will not be able to use their bodies correctly.
This can lead to them becoming heavy in the mouth, rushing, drifting through corners, disengaging their hind end, losing their length of stride, becoming tense or anxious, disuniting, struggling to go forward, struggling to jump and more.
For rider's who sit unbalanced in the saddle it is recommended that you have dressage bio-mechanic lessons, that you check you have correct stirrup length (your stirrup iron should rest close to your ankle) and that you, yourself, are sound in your body and able to sit correctly.