In Tantra, sexual energy is used as the ignition for firing the Kundalini force, the body’s biological life-energy system, merging it/you with universal energy. Mystics and metaphysicians call this reaching or achieving Godhead, Nirvana, Samadhi, Mooksha or union with Divinity.
However, unlike Taoism (which stemmed from ancient Tantra) that says bring your energy inside for longevity, Tantra says let it go…let it all go! There is no reason to hang on to anything if eternity exists.
In Tantra, sex is used as the cosmic union of opposites to create the polarity charge, or potential, that connects with the primordial energy from which everything in the universe arises—the totality of ALL.