(why doesn't MS market this rare, actually useful feature??) and someone made a GUI frontend to make it easy to use

pictured is the result of pointing it at my SSD's steam folder (used strongest compression, LZX; shall see if it has performance consequences)

lotsa details and a link to it here:
https://www.reddit.com/r/Windows10/comments/76hj26/i_tested_25_games_against_the_windows_compact/

early days yet, the tool will improve a lot. but it already enables easy access to tremendous space savings for games and probably other non-media files

(nice side effect: steam can actually download the 34GB Doom patch that's been stuck there for months)