Answer:
ATP is part of the energy cycle of muscle energy (especially non-aerobic). Your body's efficiency ref. the ATP cycle will dictate how much you will be able to do before you tire or you reach the limits set by the lactic acid in your body. So ref. weight loss, improving your ATP efficiency through a combination of training and nutrition/hydration you will increase your ability to do more (it is called the training effect) and therefore burn more calories, thus helping your weight loss.
The ATP system can be bolstered by taking the supplement Creatine Phosphate.