Found out some interesting Git Hints presented as webcasts at the site below. The most interesting part was to learn how to create empty branches on it, so a project can be functionally separated without having to kludge your working dir with several directories.
Summarizing the lesson:
$ git-symbolic-ref HEAD refs/heads/emptybranch $ git-rm --cached -r . $ git-commit --allow-empty -m "Initial commit for empty branch"
The library versus website example was perfect, but one can think about other relevant situations, like sub-projects inside a bigger project, management documentation or even meta-files configuring the repository itself (description and ACL).