what good does yoga do for the body?

In my opinion Yoga helps to stretch the muscles that might otherwise be overlooked and helps the body to relax.
It also strengthens the body due to endurance being build up while doing the poses and holding them for as many breaths as you decide on.

It just makes you feel good when your done. I like to use it after working out with weights and as a nice stretch in the evening before going to bed.

Once again only my opinion, hope this helps