Hisrtoricaly speaking, throwing knives and axes and hatchets and those sorts of things were quite common and used to soften up an enemy before you actualy make contact with them during a charge.
The discus and hammer throw, as well as shot put, are all Olympic events that recall this. Weapons themselves are found the world over, three that come to mind would be the chakram, franseca, and boomerang. I'm disregarding spears since they aren't really part of this class of weaponry.
Spanish knife forms, like El Cuchillo or La Navaja, frequently teach knifethrowing, not as a primary means of defense, but to give you extra options. They teach to throw without the blade rotating, and if you have no other weapon, to close rapidly remove the knife and get to work. Range depends on your skill, but 20ft. is probably the outer limit.
It would most heinously suck to get a large knife tossed into you, though a small one wouldn't do much.
It appears that the closed mindedness about knifethrowing as a means of combat stems from the work of Col. Applegate and other military authors. Their distaste for knifethrowing likely stems from the fact that if you give a group of soldiers a knife and some spare time they're gonna throw it, and somebody might get hurt. And the fact that the knives commonly carried weren't suitably lethal as throwing weapons, and that chucking an edged weapon at an enemy doesn't impart the same adavntage for a modern army as it did a pre-firearms force.
The "tactical" considerations appear to be quite recent. I think there are also those who just don't want the practice associated with hurting people in any context for personal reasons. If it's a sport it draws less attention from insane legislators.
However, you're not talking about a situation where you toss a dagger in somebody's back and he keels over. A few might do it, and I hear some people are starting to hunt this way.
Throwing knives really isn't that hard to do, even against a moving target, or I'm a helluva lot better with minimal practice than all these guys who do it profesionaly or with greater frequency than me. Or maybe throwing without rotating is just inherently better than doing the spinning number.
If you want to get some good practice in at hitting moving targets, get a thick dowel and chop it into several foot long sections and have a buddy run around while you chuck them at him. You can pick this up pretty quick if you have any coordination at all.
If you want to use knifethrowing for defense, I suggest doing like they do in El Cuchillo, toss it and jump the guy before he has time to recover.
