What if you are working on your computer and you suddenly become stricken with the greatest sentence, line of poetry, or phrase of dialog for your character? Do you grab the nearest scrap of paper and jot it down, hoping you don't lose it before you get to insert it into your work-in-progress?
If you are a Mac user, there is, of course, 'an app for that.'
File this under the opposite of distraction-free writing:
Grandview fills the entire screen with one word (!) or one sentence at a time. The words are then automatically stored on the clipboard for pasting into whatever application you choose.
[I've only graduated from the scrap of paper to a Post-It note or a line scribbled into my notebook.]