KriegHund: explain further, please.
I think everyones already done that for me, but OK.
A sword is much longer and unwieldy and heavy than a knife, especially in close quarters.
Thats where the knive hs a practical use- and even then it is a small use.
You see, the rifle, pistol, or shotgun can take care of anything but the most extreme close quarters, and in that sort of situation the longer reach and the space need to swing/stab of a sword is a major drawback, the knife however, with its lightweight and manueverability can stab, slash, and poke with much much shorter strokes.
Also, the knife allows for hand to hand, whereas the sword takes up an entire hand, the knife hand can also be used to strike or push or pull.
Aside from those CQC implements, the knife is also a valuable tool, where, once again, its shortrer length comes in handy for opening things or cutting ropes, etc.
Now, about that .00001%???
That would be if you are perhaps in a large, relativly empty room, and the other guy is out of ammo.