Throwing knives is fun, and throwing knives ARE fun. (So is English. *heh*) First one must concentrate on technique. Spin or no spin? (I prefer thee latter.) Then accuracy. Throwing knives as defensive tools? *meh* Not so much. Accuracy at inflicting disabling (or fatal) wounds is MUCH more difficult than with a firearm, and if a knife wound from a thrown knife is NOT disabling, then one has just handed an attacker a weapon. Not good.
Still throwing knives is as much fun as any target-plinking can be.