Complex sentence: Apophallation may benefit the amputator by serving to prevent the amputee from mating again in the near future which would result in sperm competition, or at least from mating as a male, which could divert resources from producing eggs with the amputator's sperm.
Split into simpler sentences: Apophallation may benefit the amputator because it prevents the amputee from mating again in the near future, which would result in sperm competition. The amputee is at least prevented from mating in the future as a male, which could divert resources from producing eggs with the amputator's sperm.