Is yoga useful for weight loss? YES
While the field of weight control is complex, many of the practices of yoga will cause muscles that have become tight through inactivity to become loose, will cause joints to have less pain and more range of motion, and can even help alleviate posture problems. Your body will become more supple and your muscles may even gain tone.
Also, a person who is overweight frequently judges themselves harshly. This symptom, too, can be helped with yoga.
One of the tenents of yoga is to focus on the energy coursing throughout your body; no matter how "overweight" you are. If you are interested in using Yoga for Weight Loss, I recommend this e-Book