Restorative yoga is nice for easing tension and pain from injury, increasing flexibility, or as a cool down after more intense workouts. Vinyasa and/or ashtanga practices give you a much better workout and can burn a surprising amount of calories, especially at more advanced levels.  I have burned upwards of 350 calories per hour during more intense, advanced vinyasa classes. I'm 5'4" and ~110lbs, so from my perspective that is a pretty good amount of calories  burned during an hour workout.  Basically, not all yoga is created equal and the different types of yoga can vary drastically in the intensity of the workout. Unfortunately, the fats have ruined yoga for many potential practitioners by half-assing their way through it and making it look like some namby-pamby bullshit with all the selfies they post of themselves in extremely rudimentary poses.  Edit: removed a word.