Death should be a choice.
By this, I mean that when you drop something to 0HP or equivalent, you can choose whether it is actually killed or not.
Surrender? Flee? KOed?
But what if your players don't want killing everything to be their escape?
Giving them a choice lets them be explicit about principles and tone.
If stakes are "to the death", you can be explicit about that.
Fights are legit more interesting if PCs can lose them without breaking continuity.
If you are trying to murk me, I am going to bring that same energy.
But if you can lose a fight and simply lose some ground...
And it also makes BBEG fights more dramatic, when stakes go up.
"This guy *will* kill you" gains a lot of teeth when death is not the default consequence.
It's cool to have NPCs be able to come back.