It's not about avoiding orgasm, it's about avoiding discharges of vital energies. The goal is to consciously use the sexual energies and channel them for higher purposes (spiritual i.e. expansion of consciousness) and not to scatter all that very precious energy just for pleasure of the ego only. This does not mean that we cut ourselves off from pleasure since this kind of practice provides infinitely more pleasure given the expansion of consciousness (and therefore of perception) which results from it. Moreover, we are talking here about sexual practices correlated to a love relationship (unconditional love if possible, in other words without attachment) and not about purely organic and physical sexual relations.