I started yoga to rehabilitate my knee and I love the benefits for my body. But the real reason I keep at it consistently is mental.
It is a common misconception that the goal of yoga is to get more flexible in the body. Now it is true that some people try yoga in the first place in order to get more flexible. And that's great. Flexibility can help prevent all sorts of injuries and as one of my yoga teachers was fond of saying "a flexible spine is the fountain of youth".
Yoga also makes the mind more flexible.
"In fact, according to the ancient teachings, the main goal of yoga is to influence the state of mind."
- Gary Kraftson in Yoga for Wellness p130.In a very real way, yoga can help people feel better about themselves, gain clarity about their life, and help them prioritize and become more effective in their actions.
Personally, I find I am much more focused and clear-headed in general. It makes me feel more grounded. I experience less stress in situations that previously stressed me out.