the main reason I would do it is either because I wanted to store them in different places, for different uses (eg, one to carry, one in the back of the car, one in a BOB, one spare to replace any of the others that need replaceing)
or for frost's mora knives, which can be had for cheaper if you buy them in bulk (5's I think) but are still cheap enough not to break the bank, so I could have several stored away as spares, or maybe play around with modding a couple.