In my experience, pen-and-paper helps me resist the urge to “just get started already”.

I don’t know why, but when I’m in the design-phase with a keyboard in my hands, I think I get too excited about building things and go straight to the text-editor to “hammer out the details” in code.

Away from the computer, I’m much more likely to complete a thorough design. And pen-and-paper remains my favorite tool for working on ideas that are too big to fit in working-memory.