The asanas function at many levels. They have an obvious effect upon physical well-being by releasing muscle tension, strengthening internal systems and releasing stiffness in the joints. Those who already study yoga are familiar with how asanas facilitate the flow of prana into the body and how we can work with/or control physical, mental and emotional pain. Yoga asanas are concerned with the health and beauty of the organism as a unified whole. The asana practice promotes a stable nervous system and an ability to sit for periods of time without discomfort which is necessary for mediation. Patanjali in his Yoga Sutras only refers to asana as a posture for meditation. Asana is not a particular posture but a state. Within the asana itself we find strength and firmness as well as pleasantness and comfort. The definition of asan is any comfortable pose.
Everybody is unique therefore the asana practice should arise from an internal place rather some external idea of how the posture should look like.