Edging must include a factor of random outcome. To know beforehand that he will only be edged, then denied, will lead to the male losing hope. While this is effective at crushing any remaining hope in having control of his own penis, losing such hope can affect the quality and responsiveness of his erection, not to mention erode his mental state. If he never knows how edging will end for him (orgasm, ruined orgasm, cbt) he’ll continue to hold out hope and be fully responsive. The same logic also applies to edging a female submissive.