From The Economist, 19 December 2002 (accessible here, but you probably need a subscription to read the whole thing):

Knowledge workers take notes not in order to store information, but because the process of note-taking helps them to learn. Once taken, notes are rarely reviewed. According to a study of research workers reported in “The Technology of Team Navigation”, a paper by Edwin Hutchins, a psychologist, while 64% kept their notes for years, 44% hardly ever referred to them.

The relationship between workers and their clutter is similar. People spread stuff over their desks not because they are too lazy to file it, but because the paper serves as a physical representation of what is going on in their heads—“a temporary holding pattern for ideas and inputs which they cannot yet categorise or even decide how they might use”, as Ms Kidd puts it. The clutter cannot be filed because it has not been categorised. By the time the worker’s ideas have taken form, and the clutter could be categorised, it has served its purpose and can therefore be binned. Filing it is a waste of time.