In magick we manipulate a certain amount of energy into a desired direction; for that we specify a goal, raise energy and point it into the wished direction (release the energy) to achieve a manifestation in our physical reality. In sex magick we basically focus on a goal by affirmation, visualization etc.; we raise much energy through prolonged sexual arousal and we release the energy at the moment of orgasm. The goal in sex magick can be the achievement or attraction of anything wished in the physical world, like a new house, a better relationship or a healing. It can also be the charging of magickal tools or talismans. And the goal can be spiritual development. This controlled form of love-making for higher purposes is often mentioned as the ultimate explanation of Crowley’s famous statement "Love is the Law, Love under Will." By love Crowley meant the uniting of the opposites masculine and feminine, active and receptive, and not so much romantic love.
That sounds cool. I must say that the very idea of practicing visualizations during sex in order to achieve material or spiritual goals is an attractive one. Human beings are often short sighted when it comes to contemplating the end results of our biological compulsions.