Working on thoracic spine rotation is often overlooked in a training program and/or rehabilitation program. Decreased t-spine mobility can contribute to shoulder problems and cervical problems. Increasing t-spine rotation can assist in improving proper movement.
There are multiple exercises that can be used to improve t-spine rotation but one thing is clear: The rotation must not come from the lumbar spine. Don't just take my word for it though, many other professionals agree. As Mike Reinold states: "Mobility must come from the thoracic spine and NOT the lumbar spine". Additionally, Shirley Sahrmann has said in her book Diagnosis and Treatment of Movement Impairment Syndromes: "The thoracic spine, not the lumbar spine should be the site of greatest amount of rotation of the trunk… when an individual practices rotational exercises, he or she should be instructed to “think about the motion occurring in the area of the chest." (pg 61-62)
So why the quadruped? Well, putting your hips in a position of flexion can help aid in decreasing the motion coming from the lumbar spine. Note that if your like me and lack some hip flexion mobility then this is an exercise you will have to ease into, as I still substitute slightly.