I have always been fond of the use of hand sketching and rapid iteration with trace paper, and I consider it a much more effective way to process different ideas quickly without the cumbersome entry process into the computer. That being said, computer technology draws nearer everyday to including authentic manual input into the everyday workflow. This includes things like tablet screens as well as an understanding of the universality of vector geometry across many platforms and mediums.
concept or construct
I am a strong supporter of drawing of imagining as well as drawing from observation. It is often the details learned through observational drawing that inform the quality of conceptual drawings when there is nothing of physical interest in view at the time.