What is the purpose of deep breathing?

Reduce stress: Deep breathing exercises can reduce stress levels, reduce panic and fear and helps you think clearly. Deep breath stimulates parasympathetic nervous system which slows down the heart rate. Apparently breathing can lower high blood pressure too

Detoxifies the body: Deep breathing cleanses the blood, pumps the blood to all parts of the body, and flushes the toxins from your body.
Builds lung muscles: Deep breathing exercises strengthens the lung muscles and improves the supply of oxygen to your body. Due to our lifestyle we generally inhale less oxygen, hence deep breathing assures you get sufficient oxygen. Lack of oxygen is also responsible for tiredness and lack of alertness.