Another possible use for bishops/cardinals is as spies. They don't tend to get assassinated as often as emissaries (though some provinces seem to love murdering these guys), and of course they're not affected by borderforts or counterspying agents.

Inquisitors haven't been quite as nice to me. I've had several games where one of them will waltz in and start eliminating all my decent generals, and sometimes I'm in a position to need those ones. They've usually picked up enough stars that my fledgling assassination program can't take them out, especially as they move around so often and drag their pursuers through areas with border forts. Sometimes the easiest way to protect myself is to go all out against their faction and eliminate them all.

Ajax