Free-writing: warm-up or waste of time?

Last week on Twitter, someone was asking advice about free-writing: did it help for writer's block, was it a waste of words, etc.

Unfortunately, I lost the thread and didn't get to see the consensus among responders. Some people felt that free-writing is a waste of time; it wastes creative energy and wastes precious writing time that could be used on a specific project.

I don't think it's a waste of time, but I also don't free-write in the traditional sense. Most of the time, when people talk about free-writing, they are talking about sitting down at a blank page and just writing, stream-of-conscious style, whatever pops in your head. No guidelines, no expectations, just write.

No thanks. That would never work for me. I find the blank page far too intimidating.

What does work for me is "prompted" free-writing. I start with a word or a prompt and then brainstorm (and yes, sometimes stream-of-conscious scribble) from that prompt. I get a lot of story ideas that way. The novel I'm currently editing came from a prompt, and another novel (that I should someday get back to working on) about spiders invading from space came from a prompt (I remember the prompt: "write about a spotted cow"--trust me, it all fits, lol).

On Sundays, I collect prompts from all over the web and save them into files. I now have nineteen of these files, each one over 200 pages long. I should never run out of things to write about.

Then, during the week, I warm up by free-writing to a prompt before getting down to the regular business of writing and editing each day.

What about you--do you free-write? If so, do you prefer to leap blindly onto the page, or do you prefer a prompt to get the ball rolling?