Semen retention is only one aspect. More important is to convert its energy component into higher forms, retas (fluid) to tejas (heat) and ojas (electrical) to viryas (spiritual). It is literally the transmutation of the prithvi or earth element through water, fire, aerial, and eventually Akash, the original substance. That is why Sri Aurobindo says that a Brahmacharya in the form of complete sexual mastery is indispensable for the physical transformation. Short of that, one must have a mastery over the sexual impulse through samyama (regulation) and then nigraha (complete suppression). But then this energy should be sublimated into healthy creative activities and still further through aspiration towards the higher consciousness. Else it may lead to subtle forms of indulgence through the mind and imagination, which is unhealthy and even dangerous. Mere holding back of semen is not enough; a whole inner change of life is required for the practice of Brahmacharya.
Affectionately,
Alok Da
