That's a good one for the smart part (finding huge user data stuff not created by the operating system).
(a pity that the wonderful "Sequoia View" was not continued)
I have a fairly organized disk.
C : 292 GB, 217 free, D : 683 GB, 417 GB free.
I would get only 10 GB free with Windows Disk cleanup.
I bet the OP will see much more.