Some apps can get a bit complex and having an isolated screen at the end to document the whole thing might just not cut it.
It'd be great if we could have "Documentation" as a basic property of any object (controls, screens... collections?) where you could add some text (rich text ideally) to help fellow developpers understand what you were trying to do.
As a bonus : the content of this documentation property could be the roll-over info displayed in the object explorer tree-view (left pane) to help a new developper discover the app interactively.
And the cherry on the top : we could have print-ready "documentation view" which shows every object in said tree-view with its documentation info clearly displayed.