We all know how important breath is. It is vital to all living organisms to live, flourish and develop on this Mother Earth.. 
On the surface even if it looks like we live inside the sheath of air, we breathe just like how fishes live in a sheath of water, the process of breathing has a lot more to offer to man kind.. 
Klesha moolah karmashayoho drushtaadrushta janma vedaneeyaha..
Satimoole tadvipako jaatyaayur bhogaaha 
All the actions which we involve in our daily lives are mostly derived by the antaranga (the internal environment) which are inclined  towards various desires, vengeance, jealousy, attachment and ego (which can be termed as kleshas) which in turn result in experiencing the consequences of the actions. These consequences become the main reason for the entanglement of the human consciousness with the body, pride, esteem, status and so on. The vedas believe  it to be the main cause of rebirth.
Any species that one can find on earth are expected to be only reaping the consequences of their actions in their past lives. But it is different in human life, if the human consciousness realises the purpose of life and starts to develop control over the emotions which get stirred up resulting in the actions during life, a new way and dimension of looking into the world emerges.. this state of consciousness is called Viveka..
It is expected that humanity prevails in abundance around the individual who is a Viveki or has attained a state of Viveka..and this is exactly where the Practice of pranayama throws light upon. 
While constantly exercising with the breath, a pranayama practitioner also exercises the initial response made in the mind which trigger emotions.
If you have observed., a deep inhale is when you take to express excitement or satisfaction and it is the same depth of breath taken in but with a different pattern when one is about to express dissatisfaction or disappointment. Hence exercising the mind and keeping it awake to be able to respond to any situation without the background of emotions will help develop a capacity to concentrate all the physical, psychological and intellectual energies into the applied activity and overcoming the influence of kleshas which result in everlasting freedom of Viveka..
Note: a practitioner must start learning about the importance and influence of deep, rhythmic and controlled breaths with a steady posture before practicing pranayama. This may take months or years depending upon the commitment and lifestyle..