It could be argued that all yoga is yoga therapy as all yoga is therapeutic. But when considering this question we must consider the state of the practitioner, since yoga therapy is the design and application of a yoga prescriptive with artful, mindful and scientific precision in order to effect healthful change in the physical, spiritual and mental state of the practitioner.
Yoga philosophy is an important component of this prescription as it pertains to the intentions and the attitude of the practitioner. If we concentrate on asana the body will gain strength and flexibility. Strength and flexibility are important to health but they are not the only qualifying characteristics of a robust individual. Studying the philosophy of yoga in conjunction with physical practice improves the efficacy of yoga therapy by deepening our understanding of Self and our connection with the infinite. Illness and injury, decay and dis-ease will remain afflictions to endure, but an even temperament grounded in the philosophy of yoga will make these burdens easier to bear and to recover from.