Lightning components are built with separation of concerns in mind from the ground up. The contents of a Lightning component folder, and the contents as we know them thus far, are split into separate files for the markup (view) and JavaScript code (controller). They are all grouped under a single subfolder. This is a clever way that Salesforce uses to get us to really consider the way we engineer our Lightning code and how our components interact.

As with most things in engineering, separation of concerns is not a given by just using the technology alone. Some aspects are enforced for you; other things are subject to guidelines and good component design. If you get it right, you will not only get reusable, robust, and enduring UI components within your application UI, but also within the evolving Salesforce containers, as well as for the ever-increasing number of mobile devices, and even for integration with third-party websites if needed.

Keeping in mind the separation of concerns is as vital when developing a rich client application as it is when engineering your application's backend business logic.