Breathing reflects vitality, emotions and wellbeing.
Breath practice is included in most sessions & all Hatha yoga classes
Breathing is controlled by the respiratory centre in the brain stem and generally is not something we have to concentrate on. However, early in life, breathing rate and depth become closely linked to emotions and personal stress response patterns. 
Most of us don't breathe well or efficiently..
By changing breathing patterns it is possible to change the way we feel. There are many breath practices which affect, encourage, balance and change a state of being.
Changing how we breathe changes how we think and feel - quickly.