@madsikat Read Crin's guide on save files to make an informed decision as to what you delete -
https://sims4.crinrict.com/eng/2014/09/save-games/The Tray folder contains all the items saved to your Library in the game such as lots and households. If you delete them they will disappear from the Library.
Do not delete any items in the Sims 4 app.
The Sims 4 Packs contains all your DLC. If you trash it you will need to re-download all your packs again -
https://answers.ea.com/t5/Technical-Issues-Mac/The-Sims-4-macOS-Notarization-FAQ/m-p/8876253#M29009 
