It's worth mentioning that while we do have changelogs supported in the readme.txt file for the plugins directory, there is a size limitation on that file. So, very rarely, changelogs kept there will exceed our limits. In such a case, I recommend to people to make changelog.txt files, or just CHANGELOG files and copy older entries into there as needed.

Knowing what changed is important, and the readme entries are meant to be a sort of higher level view, readable by users and sent as part of the update process. So, keep them simple, make them understandable, and there's no need to detail exact code changes made. High level overview, sort of thing, works best.