Windows "File compression" not working?

So I used the built in file compression on a few large folders in 2 of my other drives (D:\ and E:) and waited about 4 hours for the process to complete but noticed 0 difference in change on my drives' free capacity. Isn't file compression supposed to LOWER the sizes of those files and free up more storage? What am i missing?

Submitted October 01, 2017 at 01:16AM by BestServerNA http://ift.tt/2xFEFVw