For me it depends on my pre-game "rules". For instance, started Spain on VH/VH last night. All muslim prisoners are to be executed, all game-Reconquista RunAmok game. (Gave myself other conditions such as letting my popescale drop below 5 after diplomatic contact equals a loss, must conquer New World, etc). Will have this rule in a Hungarian campaign I plan to start too where instead of chivalry I will emphasize dread (Hi Valddie ol pal! My o my, what pointy teeth you have....). Haven't decided if the Hungarians will extend such harshness to the ERE, though, as of yet. I am planning a Merchants of Venice Campaign in which summary executions will not be allowed (bad for Bizniss m"lord!), though executions will probably happen frequently as every time regardless of situation they will be offered ransom. That regime will be Mercantilist to the core. Too bad they nerfed bribery to the point of uselessness...

So to answer original post, depends on my personal rules for that campaign.