I've seen a number of questions/blog posts about setting up a Git repository withe Drupal Core and Contrib Modules as submodules, such as [this question on Drupal Answers](http://drupal.stackexchange.com/q/9753/134). My questions is what advantages do you get from this kind of repository set up? Many people say things like "core and module updates are really easy." But what makes this approach easier/better than have a single repository containing everything for the site and using Drush to update Core and Contrib, then committing back to your repository? I can see this being great for contributing to those projects since each module is a separate repository, but what benefits does to provide when focusing on building your own site?