Last night I read that conscious breathing into an area of the body helps to expand and soften that area. This increased softness enhances sensitivity because your nerves are more enlivened, and your circulation in that area is improved. Conversely, if you block the flow of breath, you harden the inner and outer bodies, and lose sensitivity. Also, the breath helps to loosen the body, so blocked or stored emotions can be released naturally.
How often have you practiced yoga... become totally in tune with nature and then felt so much joy you could almost cry? It's happened to me often... almost like my body went somewhere deep and cleared out something I had been holding on to. Sometimes, while in meditation or during pranayama, an old memory, one I didn't even realize was still in my brain, comes to the surface... it's shocking how surreal and detailed they are. When this happens, I feel so much lighter and aware. I believe this is a result of conscious breathing.
I also read that for poses that generate intense sensations, the breath can be used to help to lessen discomfort, thereby allowing the poses to be held for extended periods. Increasing the power of the breath fuels the internal fire and gives you the ability to dance on the threshold of discomfort without reacting. In this way, you can meet any internal resistance with equal power. By using the breath to help you cultivate courage and steadiness, the threshold will slowly expand outward, thereby reducing the uncomfortable sensations in your pose.
I know from experience that this is completely true. How many times have I shared with you that I felt intense heat in my body... usually while meditating for a long time or while holding a difficult asana for a really long time. How many times did I mention that I sent prana to that area... that I breathed deeply and focused all of my attention to that area and then BAM... the discomfort went away? It's amazing.
I also became aware in my reading that in some poses, such as deep forward bends or deep backbends, the diaphragm gets compressed making breathing difficult. To reduce resistance to this uncomfortable situation, soften and quiet the breath.
And of course... always, always, always, breathe through the nose in all instances when practicing asana, except in Simhasana.