Namaste Y-Y
In classical yoga, bandhas was traditionally viewed as mudras and it was only later that bandhas was given a space of their own in the yoga curriculum. So I would like to go back to that classical root of bandhas to explain my understanding and personal experience of these powerful mudras.
Mudras are described by Swami Satyananda as “subtle physical movements which alter mood, attitude and perceptions and which deepen awareness and concentration.” Seen in the light of his description of a mudra I would like to apply this to bandhas as this has been how I was taught by my own teacher and what I have come to experience the bandhas to be, “subtle physical movements” which have a great effect energetically on the physical body as well as the subtle bodies.
I have been taught to teach the bandhas separately from asanas just after pranayama and before relaxation and meditation. My own teacher felt that it was important to feel each bandha and its affect on the granthis and on the physical as well as subtle bodies as intense as you can, without having to worry about the asana you are in. Just one thing I would like to mention here is that my own teacher only started to teach the bandhas to me after about 5 years of practice. Whenever I asked about it, she always said wait, your are not ready yet.
However, you can perform the bandhas while in certain asanas as well, but I think you have to go back here to the style of yoga you practice and see how they prescribe it or to your teacher and hear what he/she has to say, what is their understanding. Performing the bandhas while in asana might be something that you would attempt much later in your yoga practice, I myself have only recently started to combine mudra while in asana, but I am not very satisfied with the lack of effect I experience, so I have stopped doing it while in asana and focus on a separate bandha practice again.
Hope this helps.