So I have noticed that the windows feature upgrades create a Windows.old directory and when you try to delete it, the system pops up an error stating some files are in use. Windows is not using up twice as much hard drive space. 25GB+- for the Windows Directory and 25GB+- for the Windows.old directory. Is there a reason for this? Is there a way to delete this directory. is this going to be the expected configuration going forward for Feature update? - Currently on 1809.
Its used in case you want to roll back to the previous version of Windows. If things are stable you can run disk cleanup and select the clean system files option. It will give you the option to delete previous installations. This is the only way i know of to safely delete this folder. The windows.old folder has been around for some time. I think Microsoft started using it when Windows 8 came out.