Getting recommunicated

[drone]

Indeed. Let's not go there.

[gollum]

In any case, the threat of excom. never scared me much unless i was too big, like the HRE at the beginning and any other faction that has become too large. However sometimes its just so much better to play the Orthodox/Muslims. True the catholics will probably all together turn against you when starting becoming big and send crusades to your lands, but you don't have to worry giving word to anyone and can beat all of them to a satisfying pulp :)

[drone]

Something I've always wondered about: apart from the big target that gets put on your back, what is the penalty for being excommed? I've always assumed you get the standard unhappiness in your provinces as if they were a different religion, and that was that.

[gollum]

Yes indeed, that's what it is. Basically the catholic flock becomes discontented and that can bring rebellions in provinces that are either recently conquered or underdeveloped hence containing fewer happiness buildings.

This means that you either need to reduce taxes or commit more garrisons or both for keeping the population happy that both reduce your income and also deprive you o being able to concentrate your forces for best effect to the theaters they are needed.

I am not sure if it has a loyalty hit on your generals and contributes in civil wars directly.