I’ve purchased/owned double of a knife twice.
The first time was when I had a basic stock Benchmade Mini Grip that I EDCed for a little while and then bought the Doug Ritter version which I outfitted with OD green micarta scales. I got the Ritter because I enjoyed my Mini Grip and everyone told me the Ritter was even better. I liked the stonewash blade, but the rest of it never sat as well with me as the original. I think I sold both within a short time frame from each other.
The second time was last year when I bought a second Benchmade Bugout. I had been EDCing the original blue version since it came out in 2017. I loved the knife, but sometimes I wanted to carry an OD green version for variety and to match my clothes/mood a particular day. So that’s why I bought the ranger green version as a second. But in the end, I felt a higher connection when only having one knife to carry and use everyday. It gives you a different bond so to speak. So I moved the green one into my safe, available to use as a replacement if something were to happen with my blue one. Recently though I realized it was just sitting there for no reason, and I knew I could obtain another Bugout easily if something were to happen. Thus, I sold the green one, and now the only knife I own is the blue one.
For multitools, I still own duplicates of my Leatherman Wingman and I used to own duplicate Leatherman Waves. I had a Wave in my truck and one in the house until I sold it. Currently for my Leatherman Wingman multitools, I keep one in my Jeep and one in the house. The house one used to be in my hiking pack, but I didn’t need it so it got repurposed to the house and the second Wave was sold. I had/have multiples of those because multitools come in handy, but I don’t want to carry one. Thus, I strategically place them in each vehicle and one in the house. Although the one in the house could probably be sold because I have a tool set in the garage.