Awareness of breath is often repeated in meditation and yoga circles. Intellectual knowledge is irrelevant to our well being unless we integrate knowledge. Thus, our awareness of breath must go beyond head knowledge into the realm of our experience.
Correct breathing begins with an exhale. This means your default position-how you find yourself when engaged in activities-should be with lungs full of oxygen. For this resons, athletes are trained to act in sync with the exhale. With lungs full of air, the mind tends not to wander. With lungs empty, ruminating mind begins chattering.
Holding the breath can be an effective strategy to keep us in the present moment, as long as we remain conscious that we are doing it, and why. If you train yourself to hold your breath as a default position, you will discover a whole new set of problems develop. All psychosomatic change will produce a result. The conditions of that result (desired or undesired) depend upon a continuing awareness of how our thoughts and actions influence experience.
Tantrics are often reluctant to share techniques because without discipline and consistency they can be harmful to the physical body. This includes advanced nostril breathing.
In many ways the subconscious is already doing a fine job keeping the body running. How much do you want to compromise subconscious behavior? Put another way, if you could devote your concentrated attention to anything, why devote it to something the subconscious is already doing well? You don’t have to tell your heart to pump or make any of the millions of decisions to keep you alive, so think very carefully before you start tinkering with what’s already working or you may mess it up.
Like all strategies, unless they are constantly developing, they can turn from tools into weapons. Intentional repetition loses its effectiveness when it becomes habitual, which is why we must constantly introduce new challenges to our practice.
Tantra is not about quick fixes but about cultivating mastery, which is an ongoing task.
Aperture of Brahma 