Git is much more modular and flexible than SVN. If some developers only need access to a part of the repository, you can make it a submodule (i.e. a independent repository which is aggregated by your main repository). It is much easier to grant access to a different repository than to a single directory inside a filesystem.
It is a common practice for APIs or plugins to be separated from the main repository. For more information, have a look there.
Last point, software like Gitolite (the one I use for my own projects) and Gitosis (the one we use at work) make the administration of git repositories very easy.