The document discusses lazy loading in EmberJS applications using Brunch to improve performance. It describes dividing code into a main file containing globally necessary components and route-specific files containing controllers, templates, and other dependencies. Routes specify which components to asynchronously load using require after the beforeModel hook. An example Brunch configuration, LazyLoaderMixin, and route are provided. Results from a test site showed the main app.js file decreased significantly in size, and page load times improved by around 5 seconds.