So anything you have in your library, sends a bunch of files (7 files for a lot, not sure how many for a household) into the tray folder. Documents/Electronic Arts/The Sims 4/Tray I found this out just by playing around when I was adding a new lot from TSR. So I went into my library and deleted all the extra households and lots that I had saved and sure enough my tray folder went from over 600 files down to about 150. Then I started the game up and the initial loading screen, with the big plumbob and the below it says things like reticulating spines...well that was not nearly as long, in fact it was almost instantaneous that the game actually started. So here is the thing. If you find a lot on say MTS or TSR then yeah, it has to go into tray and fills that up. But if you find one in the gallery, there is no real need to save it to your library and fill up the tray folder. It is already in the gallery which you can search any time. Of course there is the possibility that a favourite lot or household may be removed from the gallery by the creator, but chances are small, and there will always be other lots or households. So if you have a ton of stuff in your library and find the initial load takes forever and you have some lag during the game, try trimming out all the stuff in your library you can stand to do without. Seriously it makes a very noticeable difference. additional note: the sims that are preloaded into the library by EA unfortunately can't be removed even if you will never ever use them, so they are what accounts for the 100 or so tray files that you can't get rid of.