Our hair is alive: it regulates the inflow of sun energy into the body system. In Kundalini yoga, we are training ourselves to be aware of and to master our subtle energies.
“Wearing a head covering enables you to command your sixth center, the Ajna Chakra. Covering the head provides a sense of containment and focus while practicing yoga or while doing work that requires clarity of thought. It literally helps "keep your head together." Covering the head creates a focus of the functional circuit of the hemispheres of the brain, and tunes the neurological system…”
Head coverings of any kind are useful for a meditative practice. Turbans in particular are useful for holding energy in, and for creating a meditative focus at the third eye point (brow point). In addition, the turban provides a nice cranial adjustment. Some teachers wear a turban or head covering for these yogic reasons alone.
The skull is made up of tiny bones that are constantly moving even if only by micromillimeters and the degree to which they move impacts levels of calmness or anxiety. Covering the head stabilizes the cerebral matter and the 26 parts of the brain, which are interlocked with the neurological system and electromagnetic field.
The benefit of wearing a head covering is that when you wrap the 5 to 7 layers of cloth, you cover the temples, which prevents any variance or movement in the different parts of the skull. A head covering automatically gives you a cranial self-adjustment.
[From The Aquarian Teacher: KRI Teacher Training Level One Manual]