Alternate nostril breathing, has the intention to cleanse the energy channels (nadis) of either side of the body.
the Nadis are channels, there are thousands in the body. Three of them being the
SHUSHUMNA ( travels up the centre of the body at the spinal column)
IDA (travels the left side of the body)
PINGALA (travels the right side of the body)
The IDA and PINGILA consistently join at the chakra energy centres as you travel up the SHUSHUMNA, toward light, or enlightenment.
What I know about Nadi Shodhana, is that if I practice gently when I am stressed out it has a pretty quick calming effect. As I practice more and more consistently, it has become a more consistent calming effect. I love to practice Nadi Shodhana before meditation, and before my posture practice, as it helps me find a more meditative state.
Enjoy this beautiful Pranayama ( breathing excercise) !