For efficiency and convenience, some Drush commands can work without first bootstrapping a Drupal site, or by only partially bootstrapping a site. This is faster than a full bootstrap. It is also a matter of convenience, because some commands are useful even when you don't have a working Drupal site.
For efficiency and convenience, some Drush commands can work without first bootstrapping a Drupal site, or by only partially bootstrapping a site. This is faster than a full bootstrap. It is also a matter of convenience, because some commands are useful even when you don't have a working Drupal site.