How do you know when to CAD vs draw up on paper quickly

[CamFam1]

Thanks for all your guidance everyone. Please consider another dimension to the question.

If you are running short on time, when would you come to a point where you would say do it in paper and pencil and forego putting pressure on CAD so you can have a robot rather than possibly risking not having a robot?

I see how it's ideal to CAD. When do you let it go and try using paper and pencil? Have you had any experiences like this? How did it go?