Well, this makes me wonder how I've ever gotten by not carrying a knife around with me.
About the self-defense thing, though—where do you guys live that you need to consider such a thing? Detroit? East L.A.?
And can't you get in big trouble for carrying a concealed weapon? Isn't it actually, you know, against the law? Or is that just guns? You're not advocating illegal activities here, are you? Just wondering.
I looked up some CA knife laws since this was posted and this is what I arrived at. Knifes which are are assisted (not butterfly knife, switch blades, or spring loaded) legal in most places. Blade size doesn't matter with the exception of L.A. It's not against the law and if you were indeed concealed carrying it, a cop would have no reason to see it unless you were involved in some sort of crime or run in with the police.
I am a geek! But I still carry a knife and don't live in the best part of town. That said, I
would never use the knife as self-defense. If I saw someone pull a knife in a fight, I am most definitely running or deescalating the situation. There are people who are skilled in knife fighting and self-defense who say they rather have someone pull a gun on them in a fight then a knife.
It's more for EDC (everyday carry) such as opening mail (cutting all the envelopes of artisans, mech related stuff, etc. i get

), working on my car, cutting/depressing boxes etc.