Anything you pick up and drop or place is remembered. The biggest problem is if you tend to be a pack rat and save all sorts of books, weapons, alchemy ingredients, potions, ect you will eventually have a very large save file. Best to sell off everything you don't absolutely need. I've never had a problem with bodies from dead bodies disappearing as long as I don't touch them. If I don't interact with them they disappear with the body. If I pick them up and move them or put them in my inventory and then drop them they won't go away.

10.3 MB after 153 hours.
I done the civil war.
I done lot of quests.
I am at the later stage of the main quest.
I have a lot of stuff that I am not using.

So I'm seeing the pattern: if you're a pack rat, stop being a pack rat to keep save bloating down.

I cannot help it. Old habits die hard. But noted.