It's called Compactor ... (
details)
Although with the new CM having had changes done to the compression part, maybe the compression done via CM (using Windows 10 compression methods) is now as good , I dunno.
If someone can compress their content folder using new version of CM and then compress with Compactor, to see if it still makes a difference, and report back here, that would be awesome.
The newly improved compress via CM may save time not having to analyze complete content folder each time (when very large it takes quite some time).
Also Compactor can compact each car mod folder one at a time but cumbersome to select each folder, press analyze , then press compress...
The CM compress is said to prioritize newly added content, so it may be faster now. (and hopefully also compression wise it's on par w Compactor or close.)