Pranayama, the control of Prana (life force or vital energy), has tremendous benefits. The overall benefits derived from a regular practice of Pranayama greatly outweigh those derived from any other form of physical exercise, including Yoga asanas (postures). This is due to the fact that the Pranayama exercises focus on the balancing, strenghtening, and cleansing of the internal organs. The main function is to eliminate excess carbon dioxide from the body and provide a rich supply of oxygen to the blood. Which in turn invigorates the cells and tissues in our bodies. Additionally, a regular practice of Pranayama helps improve focus and concentration, which is required for meditation. The following is a natural progression:
Yoga Asanas --> Pranayama --> Meditation --> Samadhi (Self-realization)
Mastering one stage ensures success in the following stage. The above is a condensed list of Ashtanga, the 8 limbs or stages of Yoga, which includes Yamas, Niyamas, Asanas, Pranayama, Pratyahara, Dharana, Dhyana, and Samadhi. Yamas and Niyamas deal with proper conduct, and Pratyahara deals with withdrawal of the senses. Dharana and Dhyana make up the meditation portion.