Breathing is vital process for survival.
There is no alternative or option!
It is a continuous process from birth to death. The whole respiration system is under the full control of Autonomous Nervous System, i.e. it is controlled automatically by brain.
The study on number of people indicates that the normal respiration is 16 to 18 breathes per minute at rest and the quantity of air inhaled per breath is about 560 c.c. in young and adult.
The actual quantity and rate varies depending on the requirement of oxygen by the body.
The requirement of oxygen is more if the physical, mental, emotional, intellectual work done is more, it is clear from the above discussion that the factors responsible for controlling the breathing are as follows:

1. Physical activities like walking running swimming etc.
2. Mental activities like thinking,imagining, remembering, etc.
3. Intellectual functions like reading,studying, solving some problems,discussions, thinking about future etc.
4. Emotional behaviors like becoming angry, suffering from pain, sorrow,getting afraid, etc.
   All the above factors control the breathing rate and quantity through autonomous nervous system automatically.
   There is one more factor that controls the breathing rate and quantity that is our will power. This is very important as far as Pranayama is concerned.