A creator knows that creation comes out of the blue - a sudden and unexpected congealing of disparate threads into a working solution.
I think we can all agree that the environment which you work in affects the output of your work. It shouldn't be a co-incidence then, that the work spaces of theoretical physicists, graphic designers, programmers (look at their monitors!), etc are full of STUFF (as opposed to just 'stuff'). STUFF that simply looks like it clogs up space, but is actually an integral part of the creative process.
This STUFF represents incomplete ideas, fleeting hunches, and works-in-progress, each of which could potentially spring forth a fountain of new thought.
This STUFF was put there for a reason, even if it was merely the slither of a subconscious urge screaming to be heard.
Cleaning up this mess is akin to sweeping creativity out of the door. Don't do that. Make a Mess!
side-note: Yes, I do think that "messy" workplaces facilitate thinking, forcing our minds to constantly draw connections in all sorts of different directions. I also think that there needs to be some region of whitespace in people's work space. This could be as simple as a white wall at which to "stare blankly into space" (the mind is of course, drawing patterns on the 'mental whiteboard')
Both a sporadic spray of graffiti and a clean canvas are needed to create. Design your environment to fit both.