After years of manually making database configuration changes between servers on Drupal 7, I never quite grasped Drupal 8's new Configuration Management. I knew that Drupal 8 had some sort of file-based configuration import/export, and that settings.php required a config directory to be configured, but it seemed useless/broken. After chatting to the good people in Drupal Twig, they revealed how easy and useful it was.
With the advent of Responsive Web Design came Responsive Images, and its champion, the Picture element. Using Picture, we can create an unlimited amount of image sizes that properly fits our browser viewport. But what about background images? Of course we can painstakenly save out multiple versions of the image with different sizes, and create CSS media queries to display those versions by hand, but who wants to do that while running a CMS like Drupal?