What am I exactly doing by following instructions here?
yum install chromium
not work without doing this?
The repositories are so you can update Chrome. The official Fedora repositories don't have Google Chrome, so Google provides a repository.
You don't have to do the command line install of the repos; you can do this instead:
Just select the RPM and by installing that RPM it gives you the repository, and if I recall correctly it installs the latest version of Chrome as well in one shot.
Edit: Oh, and I just noticed this from the page I linked to:
Fedora is very picky about what goes into the official repos, their reasons are outlined. Google Chrome is a proprietary product and bundles other proprietary software such as Adobe Flash plugin.