I've been free-writing daily, or very near daily, for over eight months now. I average about 20 minutes, or four long-hand pages, in addition to the structured writing--the stories and assignments--I do daily.
I've had a hard time convincing myself that free-writing isn't just a waste of time, a selfish indulgence, or worse.
Lately, however, I've noticed my free-writes have become less like "stream-of-consciousness" tomfoolery and more like serious "deep sea diving." For instance, I write more about writing. Character and plot-related ideas come to me more often, interspersed with mutterings of discontent or rants about the weather. I also move more easily from the creative, purely poetic to the logical and sequential, and back. I'm not sure I can explain how this happens, but I have a theory.
Free-writing by definition frees you in many ways: from structure, from an obligation to make sense, from pressure to produce "art," from all the rules of grammar and spelling. In effect, it reduces writing to a state of play. Over a long stretch of time, free-writing gets even freer. Like a clutch on a sports car, it aids the writer's ability to shift smoothly from a state of normal consciousness to artistic consciousness and back again. It actually takes both states to write well--just not at the same time.
The normal consciousness is the old busybody, the editor, who lives and reigns, to a greater or lesser extent, in every successful writer. He's the one that sits on your shoulder and says "'Hemorrhoid' has 2 R's, Dummy!" (He would know!) The artistic consciousness is the trickster on your other shoulder. He plays dumb until the editor's back is turned, and then he spins royal garments from common thread.
Free-writing makes it easy to finally let these two schizos peacefully coexist.