Unlike rpgplanet-all, which is merely developer repository for convenience and hacking around true git absence of svn:external, this repository is used as meta package: When on given version, it represents state of all dependend package (= whole rpgplanet family) in a given state (= versions).
Not very important from developer perspective, but used heavily for deployment.
Home of some scripting deployment stuff. You may look especially into pavement (for paver) which calls fab (and his fabfile).