Every time I go to a yoga studio, I wonder why there are so many mirrors.
The coach and himself can find their own shortcomings more conveniently through the mirror. Mirrors are our "good partners" in practicing yoga. After mastering pose, it is a good way to observe the shortcomings in details with a mirror. But remember, the perfection of posture is not the perfection of action appearance, let alone the perfection of yoga. The real yoga practice is based on the practitioners themselves. It is the generation of energy and aura, and sublimates the body and mind at the same time.