Well, it makes pretty much all unique NPCs immortal (unless the players chooses to slay them), so it's not very immersive. People live, people die, that's the way of life. Immersive Citizens already overhauls the NPCs behaviour, so people are less likely to die as they should flee from battle when the attacker is too powerful. Maybe it's worth considering if you use mods that make the game a lot harder like Sands of Time, Revenge of the Enemies, etc. But for Step Core I don't see the need for such a mod.