From David's review:

https://github.com/damyon/moodle/compare/MDL-55071-master~142...MDL-55071-master#diff-35b4a816e0441e6a375cd925af50752cR146 We need to justify this change for theme_clean user. Even if browsers cache it, tt is around a 15% increment in the file size. I haven't found any justification in MDL-55377

The link is broken now and I haven't investigated properly - so I just wanted to crease this issue to ensure that the production CSS sent to users does get minified. There is no need that we have to accept larger asset size for users just to support auto-flipping.