In Mosaic law, if a burglar breaks into a home under cover of darkness, i.e. his intentions are unclear, they are assumed to be violent, and if the homeowner strikes and kills them there is no blood on the homeowner's hands. However, if "the sun has risen on" the burglar, i.e. his intentions are clearly non-violent, and yet the homeowner strikes and kills him, there is blood on the homeowner's hands. From what I've read, most states' Castle Doctrine follows along these lines to varying degrees.
Sometimes the difference between Castle and non-Castle states is blurry, sometimes not. In most cases you cannot pursue an invader who is retreating, or employ deadly force upon a retreating criminal unless they are shooting at you. In other states, such as my own, no deadly force whatsoever can be applied unless you, or a minor under your charge, are unable to retreat AND are actively under threat of imminent severe bodily harm or death. You can't brandish, you can't warn, you can't chase them out, not even if you can see the evil in their eyes and know they're about to strike; they must be actively pursuing you with deadly intent. See how the need to discern the moment of decision in these cases causes even more undue stress and can cause someone to hesitate due to fear of the law, and possibly die because of that hesitation. This is why I believe Castle Doctrine, in any of its interpretations, is desirable.