The layouts array element is used to define implicit associations between layouts and views/folders, this does not mean that you need to register ALL your layouts. This is a convenience for pairing them, we are in a conventions framework remember.
Before any renderings occur or lookups, the framework will check this array of associations to try and match in what layout a view should be rendered in. It is also used to create aliases for layouts so you can use aliases in your code instead of the real file name and locations.
// The alias of a layout
// The layout file
// A list of view names to render within this layout