The Yogis' ideal is a body strong in all its parts, under the control of a masterful and developed Will, animated by high ideals.
In the practice of the Complete Breath, during inhalation, the diaphragm contracts and exerts a gentle pressure upon the liver, stomach and other organs, which in connection with the rhythm of the lungs acts as a gentle massage of these organs and stimulates their actions, and encourages normal functioning.

Each inhalation aids in this internal exercise, and assists in causing a normal circulation to the organs of nutrition and elimination.

In High or Mid Breathing the organs lose the benefit accruing from this internal massage.
The Western world is paying much attention to Physical Culture just now, which is a good thing.

But in their enthusiasm they must not forget that the exercise of the external muscles is not everything.
The internal organs also need exercise, and Nature's plan for this exercise is proper breathing.

The diaphragm is Nature's principal instrument for this internal exercise.