Yoga is fundamentally a practice of working with the mind. Most people start with the physical postures, because that’s the easiest way to start to wrap your mind around the whole process of transforming mind. But yoga is much more than just what’s visible.
So you work from the grossest to the most subtle levels, progressively fine-tuning and refining your awareness. You move the body in harmony with the breath in order to shift the energy dynamics and patterns of the physical body, which has a direct and immediate effect on the mind. Of course you can leave it at that, and be satisfied with a healthier body. There is absolutely nothing wrong with that.
But if you want to take things a little further, yoga has much more to offer. You can go much deeper into increasingly subtle aspects of interacting with your world, shifting the whole inner climate. Call it inner climate change.