When we speak of voluntary control of breath, it means firm association of conscious mind with the process of breathing. One becomes aware of each and every breath, when one breathes consciously. This, then, is a technique of steadying the wandering mind and concentrating it. Trained by this process, mind sheds its bluntness and becomes sharp enough to be aware of even more subtle objects and phenomena.
Process of breathing is natural and inherent, i.e. not an external or an imported object. It is ever ready to serve as a prop. It is neither a memory of the past nor an imagination of the future, but a real event of the present. Perception and awareness of breath enable us to live in the present moment. Besides, it is a pure and uncontaminated event, i.e. bereft of the pollution of like and dislike.