We are preparing OS upgrade from 1709 to 1809 for >5000 workstations.
After upgrade Windows.old takes between 5-10 GB of disk space.
In the MS doc is stated you can use DISM /Set-OsUninstallWindow to defile how long user can roll back.
But after this period (default=30 days), does Windows also *automatically* clean up Windows.old?
After 10 days , that folder automatically removed, but after then that folder exists, you can use other method described below link.