Problem
Objects in worlds start to clutter the world. These are items such as bikes, collectibles, plants, food and drinks. They can't be deleted as they are outside of a lot and even spawn on top ...
Ideas
Haven't seen a spawner being added to ZoneObjectData other then the snowglobes but I didn't test many other hoods.
Plants can be any kind.
It probably also happens with homework, instruments and other stuff if you do what's in this thread: https://answers.ea.com/t5/Bug-Reports/NEEDS-SAVES-Objects-stuck-when-placed-in-world-after-loading-a-r/m-p/14193914
Haven't had a chance to test this case.
You found some very valuable info. Currently in the process of smoothing up your guide and putting it in my blog so that's what I'm busy with :D
This is part of what I found in one of my RRs in Oasis Springs. My monitor is limited so there is more when scrolling and that' s only Chrysanthemum.
The ZoneObjectData for only this single RR dropped from 7.7 MB to 0.58 MB after cleaning. The complete Save file decreased from 64MB to 34MB. Because of this bloating of some ZoneObjectData sometimes neighborhoods couldn't be loaded.
I also forgot to mention: cradleObject_GENBook These are those books floating in the air.