Poisoned boarding tactic
During the Stygian Wars the Alpha Legion made use of what became refered to as poisoned boarding attacks. When a hit and run attack was made against an Imperial vessel often times a number of spawn, preferably those favored by nurgle would be unleashed onto the ship and then abandoned. The spawn would haunt and terrorize the decks of the ship and if favored by nurgle spread disease throughout the vessel. Thus for the cost of a spawn entire Imperial vessels would be brought out of service and laid low.