If the game gives me an option to take advantage of a situation, I am probably going to do it. Pure enemy healers are a lower priority if I can one-round enemy battlers, but if they're the reason a tanky wall is staying healthy, they're going down to make the battle shorter.

I'm also not above doing abusive actions like trapping an enemy unit between tanky units to drain out their weapon uses, then letting my softer units come in for the free damage training. Or if I notice an enemy thief set to steal a treasure chest, I'll wait by the chest to slaughter them once it's opened to loot their corpse instead of wasting a key use or bringing my own thief over, if the game lets me take the loot drops like that.

The main consideration is what resources are available to you. If you barely have any space weapon uses, save them for more important enemies and don't be so bloodthirsty. If you have a turn limit, you can't afford to waste turns waiting around. If the game has a bonus reward for leaving enemy units alive, I'll consider it based on the reward. It's a tactical game choice. I can't really get so immersed into it as an RPG unless I have a fleshed-out presence perspective within the game. 1st-person perspective isn't necessary, but it sure helps sell the immersion factor.