If you have changed the default app save location to an external hard drive or secondary drive, Windows will create three folders, namely, WpSystem, WindowsApps, and WUDownloadCache on the target drive.
You may later change your mind and revert the default save location to C:. But you may be unable to delete the leftover WindowsApps folder on your secondary drive due to tight NTFS permissions assigned to the folder. The other two folders, WpSystem and WUDownloadCache can be deleted easily.
When you access the WindowsApps folder on your secondary drive, you may see the following message:

You have been denied permission to access this folder.
And the Advanced Security Settings dialog shows the error:
Can't open access control editor. Unable to perform a security operation on an object that has no associated security.

This article explains how to properly delete the leftover WindowsApps folder on your secondary or external hard disk drive(s).Read more