After experimenting with Pattern Lab and Drupal 8 theme development for a while I am starting to see a whole new role for Pattern Lab StarterKits.
StarterKits can contain the source files and master copies of all resources that need to be shared between Pattern Lab and a Drupal theme. With these removed from a Drupal theme all that is left, basically, are the PHP code parts.
StarterKits can be used to separate concerns in a well defined way and to provide a project that can be shared by people and teams with different skill sets and roles.
StarterKits for Drupal themes can be used and developed in Pattern Lab with no Drupal installation required. Even in cases where the same people are responsible for both the PHP and Twig/CSS parts of a Drupal theme, this separation helps to improve the design and implementation of both parts.