As part of our code review process for a current project, it was suggested that rather than calling the static Drupal formBuilder function to insert a form into a custom block, we actually inject the *Form Builder service* directly into the module, and for bonus points also inject the renderer service.
 
I'd previously had exposure to dependency injection earlier on the same project but hadn’t exactly grokked the concept fully and so with a few pointers in the right direction, I set about refactoring the code I’d written using dependency injection and Drupal services.