Of the exact same knife, same scales and steel? I have done that three times, where I bought one knife and then bought another just like it.
Once was an accidental double order - I thought one vendor was out of stock so I placed an order for the same knife from a different vendor, but the first one came through. I ended up keeping both and used one of them to experiment with dyeing the bone handle and keeping the other original.
The other two times were with Case CV steel knives so that I could experiment with patinas on one knife and leave the other untouched. Of those two, I still have two Case Small Texas Jacks, Amber Bone CV. I carry one of them relatively often, the other sits in the box. The one I carry is the one I played with various patinas on. The other was the Chestnut Bone CV Peanut, and I gave the duplicate to someone. I have other Peanuts, but no duplicates.
I certainly have multiple knives in the same pattern with different handles or steels or both, or with variations in blade types. I will get drawn to a particular pattern or style, but other than those specific ones I mentioned, no exact duplicates.
I know some of the more well-heeled collectors will buy two of each knife that they buy, and put the best one into their collection and use the other one. Not a thing wrong with that if you can afford it and want to do it that way.