Freeing up space · Caches and clutter
Why does Storage Studio say some cache locations are already empty?
Short answer: They've already been cleared, by you, an app or macOS. Storage Studio counts them instead of listing empty locations, so the real findings stand out.
Because they are — either you or an app cleared them recently, or your Mac emptied them itself. Rather than list a long run of zero-sized locations, Storage Studio counts how many are already empty and keeps the list collapsed, so the things actually worth acting on stand out.
If Free Up Space finds nothing at all to do, its result banner turns orange and says it's already optimised. That's good news — look at What's Using Space for the bigger items instead.