Readability is hit and miss. Very nice to have everything written to the same standard, it makes it much easier to navigate through any project. Downside is it's pretty rough for more peripheral teams or teams working in a language that's a small component of their product. I remember for one of DeepMind's big launches the interface was all in files ending in .notjs, presumably since they didn't have anyone on the team with Javascript readability. This was 5+ years ago, though, so some of the downsides may have been mitigated.