In the prologue of The Fires of Heaven: Snatching at saidin, he filled himself with the Power, the Taint on the male half of the True Source rolling off the protection of his bonds and oaths, ties to what he knew as greater power than the Light, or even the Creator. This is Rahvin acting. He is embracing saidin after Lanfear enters his chambers. Those "bonds and oaths" sound like they would be the black cords....when Rand cuts Asmodean's cords, Asmodean flips out. Rand comments that the "Chosen" allow the DO to attach himself to them. He says that he cut Asmodean off from the Dark One, and Asmodean and Lanfear also believe that that was so. The terminology sounds similar to what Rahvin used ("bonds" and "connections"), though it is not identical, and both seem to result from oaths to the DO. This could indicate that the cords are partially to keep the Taint out.