People do yoga for all sort of reasons. It may be for meditation purposes, relaxation purposes, to get fit, to have a good posture, to make new friends, etc etc.
I'm not sure how fit you can actually be if you just do yoga using a yoga strap for example but I do know that it makes you develop really good posture for yourself.
I have yet to be really active to a specific yoga routine. The last time I went for a class was a year ago. Argh.. I really need to get myself more active. This is soo horrible. How do you make yourself like exercising? Blargh..