A Drupal site usually has A LOT of CSS files (it’s probably only Drupal sites that constantly break the 31 css file-max in IE8 & lower)
Usually a module comes with a couple of files containing defaults and other goodies, but the theme does not always need the default CSS. It can be a "little bit" annoying to use time and resources to overwrite each module's CSS, just to keep your theme clean, not to mention the unpleasant surprise if a module comes with badly written CSS.
The Mothership will help you handle this by letting you strip out css files like a true pirate and remove stuff you don't need. You can still add it later if/when you DO need it.