Patanjali Yoga Sutra — ततः क्षीयते प्रकाशावरणम्॥2.52॥

Tataḥ kṣīyate prakāśāvaraṇam॥

Prāṇāyāma helps the sādhaka to destroy the curtain that obscures the light of divine discriminative wisdom.

Just a spark of light is enough to drive out clouding darkness. Similarly, prāṇāyāma is so powerful that it can weed out the ignorance of sādhaka and his discriminative wisdom glows in full verve. That is the power of prāṇa. There is no substitute for prāṇāyāma. Vyāsa Maharṣi says, ‘there is no penance superior to prāṇāyāma as it is a marvelous tool for dehaśuddhi and jñānadīpti’. As stated earlier, prāṇāyāma itself is a great yajña according to Bhagavān Śrīkr̥ṣṇa.

The story of Hanumān is vividly mentioned in Rāmāyaṇa and Mahābhārata. He is depicted as the son of Vāyu — the God of wind. Hence he is also called Vāyuputra, Prāṇadeva. This is the first clue for what Hanumān is. He is one of the seven immortals (अश्वथाम बलिर्व्यासो हनुमांश्च विभीषणः। कृपः परशुरामश्च सप्तैदा चिरजीविनः॥). This is the second clue to understanding the power of Prāna. He is the master poet in Sanskr̥t. He was a great musician (there is a Rāga by name Hanumāntoḍi). He knew many languages — third clue. That means intellect can be sharpened by prāṇāyāma. He is very powerful, capable of killing many demons with bare hands, move mountains, rocks and huge trees (Sundarakāṇḍa and Yuddhakāṇḍa of Rāmāyaṇa). He remained undefeated forever (Hanumān was the God in the flag of great warrior Arjuna) — the fourth clue. He was very balanced and personification of humility. When untamed, he could be destructive (Laṅkādahana). When tamed, he is the best servant — the fifth clue. Then the benefits of Prāṇāyāma can be understood.