I've seen a number of questions/blog posts about setting up a Git repository with Drupal Core and Contrib Modules as submodules, such as Setting up the ideal multiple repository Drupal Site version control with a DVCS.

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?