If you develop an application with a significant degree of complexity and a vast amount of user input choices then documentation is essential to your product.
Consider the humble shell interface. It doesn't matter if you are using Windows PowerShell or a UNIX shell, the terse command prompt gives the user an empty page. Knowing what options are available is key to using any product. Man pages allow *NIX users to find the directions and PowerShell offers Get-Help. Imagine trying to use either shell without those, or the vast online documentation online.
Your application might not be as freeform as a shell interface, but if the number of buttons, icons and menu items is large then the user is back to an irritating choose your own adventure through your UI.