Do you mean the duped items, or just items in general, as aforementioned keeping duped items can put you in some serious hot water. Just make sure you don't cause any further issues as the duped "items" may be corrupted.
I've experience this quite alot, this happens when the server crash and the world itself is rolebacked but not player inventory. Meaning it will dupe items if you grab items from any storage type block/mine blocks a couple min before the crash takes place. This happened to me quite alot, this can also do the opposite, if you store items/place blocks then it crash, those items is as good as gone.
As long as ur not trying to intentionally crash the server to dupe items or duping them on purpose it's fine. To be safe tho try to not take advantage of duped items cus duped items are still duped items But noones gunna ban you for not noticing that you have one extra iron than before
I actually hate the crash, I've lost more items than duped...well it's a test server so nothing I can do about lost items. And ofc i throw away the duped items
