I'm sure that duplication is a personal thing, depending on several factors. If you're a uniform dresser on Team Color with limited time to do laundry and plenty of storage space, I would guess you're more likely to duplicate than if you're Team Silhouette with a small budget and a tiny closet. And, of course, everything in between.

I duplicate both intentionally and "unintentionally". For example, I have doubles of the two black tops in Finds. They're my go-tos for FFBOs. Having a second copy of the silk tank helps prevent laundry backups, since it's hand-washable. I wear the long-sleeved top both for my work-at-home FFBO (uniform) and, sometimes, as a sleep shirt. This is intentional duplication that works for me.

I also have duplicates like the two silk tunic dresses, where I searched high and low for a HEWI dark floral silk top, finally found one, and then was so happy with it that I bought a second when they went on sale. I wear them both, but I know in my heart that the second one was a mistake. I don't love it quite as much as the first, and it horns in on a wardrobe niche that was already filled perfectly well. This is a personal thing. For some, such a purchase might bring much-needed variety. For me, I would have been better off investing in a completely different silhouette or upgrading an essential to higher quality. I'd call this an "unintentional" duplication, but really it's just thoughtlessness on my part.

How does duplication play into your wardrobe strategy?