I am playing with Castille, and attacked Morocco. When I attacked the Pope called for a crusade. I conquered all of their provinces, but instead of sueing for peace I left 10.000 cavalary men who kill any single revolt. As they are not christians, they do not cause any War Exhaustation, and thank's to that I can raise war taxes whenever I feel like it (although I haven't done it usually). Therefore I am getting crusade bonuses: +30% manpower, + 10% National Tax, and when I feel like it I can raise war taxes +50% NT (paying WE, but reducing it when I am at peace with the European countries). It is silly that the effects last so long. From my point of view and if you are a huge country is interesting to call for the crusade using this tactic.