This sounds good in theory but in my past 3 games this is a mixed benefit.

You can only launch a single crusade, and victory nets you 10 k worth of florins, this is great if you only have 2 cities to upgrade, but when playing as italian factions this barely pays for two large cities to upgrade, in fact it dosn't.

So far Milan and HRE both seem to get excommunicated, it has it's benefits, and helped me take out milan in two different campaigns. Yet usually it's financial gains are minor, as if you attack HRE or milan's outlying provinces your once again stuck amongst french or hungarians, who both seem to attack you just as oftne.