Freeing up space · Caches and clutter
What is the Known quick wins section in What's Using Space?
Short answer: A collapsed list of well-known caches and leftovers, with a count of how many are already empty on your Mac. It's collapsed so empty locations don't crowd out the real findings.
It's a collapsed-by-default list of the well-known caches and leftovers that commonly take space on a Mac, with a count of how many of them are already empty on yours.
It's collapsed so a long list of places with nothing in them doesn't crowd out the real findings above it. Expand it to see each location and its size; the ones Storage Studio can act on are cleaned through Free Up Space.
For what the rest of the window shows, see What is What's Using Space?