Quote Originally Posted by Grond
Is there ever a reason to have a high zeal? It seems like you want it for other factions, so your crusades can come by and pluck their best people, but other than excommunication/bad king vice, it doesn't strike me as being useful for anything.
It is usefull for Muslims (helps Jihads and it slows Christian expansion down due to low loyalty) and in foreign territories if you are Catholic (fascilitates crusades and inquisitions and it can really wreck the HRE if they are excommunicated again).