Agreed, for me this is a killer feature. Being able to just download the gitlab-runner executable (1 file) on mac/windows/linux and register a private runner - even on gitlab.com - and the simple configuration of CI builds, with the deep integration of CI results in the whole gitlab experience (commit browser, merge requests ("merge if CI succeeds", etc)) is best of class.

Edit: I'm not usually bothered by downvotes but I'm curious about what kind of agenda whoever downvoted this has.

Self hosting is a big one. Having control over your source code and a core component to development workflow is important to some people.