Have you ever noticed how having additional clear surfaces can help make a room look less cluttered?
I recently added two standing trays to the side wall in my office, to relieve my desk of opperational clutter. One is for incoming things I have to process, the other is just for things to file. There used to be a pile of stuff to process where the trays are standing now. Now there is stuff under them - mailing prep for MidFanzine - but that section of the room looks much more tidy. I think it's partly because the "to be filed" tray is empty - having the clear surface makes the whole space look better.
Possibly my sense of "cluttered" has to do with affordances. A floor with piles of papers on it looks cluttered because it doesn't afford walking. Since trays or a table already don't afford walking, putting stuff underneath them looks less cluttered - and the two trays with one clear looks less cluttered than one tray looked by itself, when full. Because it affords putting stuff on.
It's a theory. :)