Player crafted items (like leather vests, etc.) and player spawned items (like bones, meat, feathers that spawn after skinning and quartering a body, paper from opened boxes, etc.) do not despawn properly (even if they are ruined). I don't know how long it takes for them to disappear but after 3 days bones and meat still didn't despawn. I killed a chicken near my base, took only meat, everything left on ground, came back 3 days later to my base and everything was still on ground. This probably will have some major impact on server performance after longer time (hundreds or maybe thousands of items staying on ground all the time). Some players say that if you will pick it up and drop it on ground it will despawn properly, however I can't confirm that (tried it and item was still on ground 24h later).