This is, I guess, really a continuation of the "process" discussion. My first drafts are always so influenced by the reading and on-the-ground research I do while writing. The smallest thing can steer a book off on a new course. While reading for a novel I've been suddenly steered to write about hair salons and restored muscle cars. While walking a neighborhood in Minneapolis once to "get it right" for a book, I spotted two seventy-something women kissing passionately and that took the story in a new, important direction. The other day I was out walking and a grouse burst out of the snow. I turned around and headed home, as it was clear I had just been handed something I needed for a scene that was eluding me.
Producing pages in any fashion possible is crucial for that first draft, but it's just as important to every now and then look away from the story.