Over at modxcms/revolution#12538 we've been discussing the compression settings and how they effect performance and optimization.
While concatenating and minifying the files is good (if done on the front end never if done on the back end) the truth is that enabling GZIP compression alone will have a more significant benefit. In other words, you're better of serving unminified flat files that are GZIPed than you are minified ones that aren't.
So anyways, I don't think MODX can automatically enable GZIP on people's servers but I was wondering if maybe it is worth a note in the docs...

https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/optimize-encoding-and-transfer?hl=en