Upgrading Drush to work with Drupal 8-dev
When I first started learning Drupal, I remember the process of enabling and disabling modules on the Modules page took for-ev-er. My laptop was in serious danger of getting hurled across the room, due to my frustration. Then I discovered drush, and downloading and enabling modules was now performed with ease instead of pain and suffering. Of course there's a lot more you can do with drush than just download and enable modules, this is just one example.