In my game of Scotland+Ireland I noticed the current Pope was pretty sinful, and that one of my own bishops was quite virtuous. I had prestige to spare, so I installed an anti-pope just to try it out. Overnight my income went from 16 a month to 38. Money was no longer any issue whatsoever, and over time I spammed pretty much every upgrade on my 8 castles. I was brought down by assassinations nonetheless, but still the anti-pope is a little ridiculous.