What is this practice doing?

Traditional yogic texts describe the human system as containing thousands of energetic pathways, known as nāḍīs. Among them, two are considered especially important.

Iḍā is associated with the left nostril and traditionally linked to cooling, receptivity, intuition, and rest. Piṅgalā is associated with the right nostril and traditionally linked to activity, vitality, focus, and action.

These are often described as the feminine and masculine currents within the body.