How does system choose between application:didFinishLaunchingWithOptions: or a storyboard to set up window?

How does system choose between application:didFinishLaunchingWithOptions:
or a storyboard to set up window?

I'm comparing the templates for a Single View Application and an Empty
Application in Xcode 4.6.3. The Single View Application uses a Storyboard,
and has a storyboard file that indicates which view to put in the window
when the app starts. The Empty Application sets up and assigns the view to
the window in the application:didFinishLaunchingWithOptions: method.
So why is the application:didFinishLaunchingWithOptions: method empty in
the delegate for the templates that use a storyboard? In this same method,
I would expect to see the code telling it to refer to the storyboard to
build and assign the initial window and view, since it is the same method
used in the other template. These delegates otherwise look the same.
I'm asking because I want to know how I can switch to using a storyboard
later if I need to and vice versa.