When you click on a list item, you get taken to that item’s details screen where you can customize it using components.
But you can also use the Details
layout for the top level of your tabs and structure that with components.
One of the most common reasons you would do this is if you don't want your tab to be a list of items, but rather a page with different things on it, like a home screen.
You can also use the details layout to create a single screen into which you place multiple components, Inline Lists and Relations to create a truly unique layout for your screen.