When not to use CCW...I think the correct answer should be to use it only in defense of self or one's immediate family. As Jeff Cooper said-- and I'll paraphrase so as not to mangle the good Colonel's original quote-- a lifelong dedication to deescalation, avoidance and deterence will help extend the length of your life. Kelcarry makes a good point-- 67 years of walking around the planet and he hasn't needed CCW. I hope that's the case for me too; however, I'm going to err on the "better to have it and not need it than to need it and not have it" school of thought.
If someone is clearly threatening me or my family, I will try to talk my/our way out of it and leave the area as expeditiously as possible. This hasn't happened in a long time, mostly due to avoidance of places where conflict is likely and having a physical detterent-- I don't think I look like a soft touch, nor as an active duty Army officer do I appear to be a small, easily defeated victim. Neither does my wife, who can bench her body weight and does more pull-ups than me. She usually leaves the CCW to me, and I haven't needed it yet.
For the classic convenience store robbery scenario- in a situation like that, unless the clerk is going to get killed, I've got nothing invested in the situation and will probably get out of there alive by keeping calm, keeping my head down, and not being a hero. Accidentally shooting a bystander or the clerk in the crossfire would be much harder for me to live with than letting a robber go free, to say nothing of the compelling need to convince a jury that I was somehow threatened by the robber to the point that I needed to kill him. If I had to shoot the robber, it would be because I was personally threatened with imminent death or harm; if he shoots the clerk, it's automatically going to a murder case for him, so why not shoot the rest of his witnesses? His brandishing a weapon would not be a clear case for me to engage him, nor would firing it into the air, but attempted or actual assault with the deadly weapon would probably push me into combat mode.
As far as home defense goes, Castle Law state or not, most of the homes I've lived in had the master bedroom on the second floor. If someone is on the second floor, I think there's a reasonable argument that life/limb are at risk. My wife and I have discussed this a few times. Household Battle Drill# 1 (React to Contact-- Intruder) is pretty simple...
1) Person closest to the child's room goes and gets the baby, then goes to the bedroom, locks the door and gets away from the door, behind cover if possible. Call the police. Stay put until they arrive and knock on the bedroom door. Keep a firm hold on long gun (shotgun) and have backup weapon (pistol) available. Shoot intruder who comes through the locked door.
2) If possible, person not in contact assumes good covered and/or concealed position in another bedroom and watches the stairs, with an angle of fire that will not carry rounds into the bedroom through the wall or door. If this is not possible, both parties take up good covered/concealed positions behind in the master bedroom, and assume good firing stances away from the door and at safe angles from each other.
3) All clear is when person outside the bedroom says the "safety word" through the door. Two code words exist: one means that it is all clear, another one means that it is not all clear and I am being held at gunpoint. Other safety condition is the arrival of law enforcement.
As I said, there's nothing complicated about this. All it took for me was short conversation with my wife and few goofy words (the sillier they are, the easier they are to remember). We say the safety words in public sometimes to describe certain situations, which is amusing and keeps them fresh in mind. Keeping a loaded weapon available with a toddler around is difficult but it can be done, safely, if the right steps are taken.
Great thread, guys.