Anyone carry a knife along with their carry firearm?

I've been looking at people ccw setups online and I see that some of them have a small fixed blade attached to their holster. My understanding is that they are considered "get the hell off me" knives, as they can be used in very close quarters when you can't use your firearm. Anyone here do this or have opinions on it? To me it sounds like something that could be practical via /r/CCW http://ift.tt/2lueFqK