Paramhansa Yogananda has a series of lectures and pamphletes which are available to all who take the SRF fellowship and newsletter.
In the lessons, he talks about energizing exercises and also insits that all disciples practice it for 30 min to an hour a day. I could not understand the reason and thought it was part of modified asanas. However, I finally have understood why it is important. For the awakened shakti to rise up through the Sushumna, completely and freely, the body has to surrender also. This step is difficult and can be achieved most easily if the body is voluntarily relaxed (or in other words, the body totally surrendered to the divine). Just because our mind and intellect has surrendered it does not mean that the body has surrendered. The body will continue to impose it demands such as need for food, sex, sleep, etc.
While talking on the subject of relaxing the body, I have realized why I have or need glasses. The eyeball is not relaxed! If one can slowly learn to relax the eyeball, keep it relaxed, eyeglasses could be dispensed off.
Bhavin