Almost everything in the saved folder can be deleted.
Double check the docs site though.
Some of the engine/project settings are stored here.
To avoid having to drill into the settings again when you restore a project you usually want to retain those files.
As far as the rest. If you have the capacity to store the files, store them. The engine is smart about what it compiles or doesn’t compile so it can save time to just keep the files on hand if you have the storage room for it.