How to check if Windows saves space or to activating space saving

Windows 10 is able to compress system files and decompress them on the fly to save diskspace.
Sometimes this is actually turned off.

To see if it is turned off and turn it on again do the following:

Go to the Admin commandline and write this to check if it is enabled:
compact /compactos

And to enable it write the following:
compact /compactos:always