I may be wrong but I think that things just dropped will despawn after a few in game days. I had stuffed aphids and mites that I placed on my crow feather bed that disappeared and a bombardier beetle dropped outside that disappeared. The purpose of the pallets and stem racks anchor those items to the game. Also, I have had a ton of grass planks despawn after a few days as I was farming plant fibers and not collecting the planks. Someone correct me if I am mistaken.