I sometimes use a crusade to attack an enemy I would normally attack just to gain the benefits (as mentioned by Ludens and others) of a successful crusade. Plus, its only $1,000 to make the marker and another $0-1,000 (depending on zeal) for the “permission” from the pope and you can usually get 3-4 good units out of the deal. I would say, why not crusade? Especially when it is a slam-dunk sure win situation.