It stretches the muscles and stimulates the circulation or blood flow. These techniques of slow movement takes grace and an open mind. Each posture is held for a period of time in order to give the muscles the full benefit of the posture. Special breathing is also important. The basis of breathing is long, cleansing, breaths filling the lungs and pushing the stomach out.
Yoga is used for preparation of sports.
Sometimes it helps people to get off of drugs. And for some, it helps them to become less stressful and more in tune with your inner soul. You become in focus with the other things around you that you haven't really paid attention to. Think of Yoga as Windex and your window is covered with stress, frustration, and your problems. Yoga washes the window and now you can see out better.