A change log is the quickest, most convenient way for users and contributors to identify significant changes in a project as it moves from one version to the next. The log exists to keep users informed.
Unfortunately, many open source project leaders have little motivation to provide a meaningful CHANGELOG file and are purely focused on shipping the code. Instead of writing clear, understandable logs for a release, many developers resort to dumping git logs, which are often rife with messy commit messages, into the CHANGELOG file.
Links and Resources:
Keep a CHANGELOG
WordPress Improving your plugin – Changelogs
olivierlacan/keep-a-changelog
