I believe any writer worth his or her pen will confess that at least 50 percent of their work is garbage. I believe this to be especially true of those who simply plop down at their PC and start hammering out text. I hold to this idea fervently. Why?
Let's look to the venerable John Steinbeck, author of classics The Grapes of Wrath, Cannery Row, and Of Mice and Men. Years ago, I read a bit of his wisdom about the creative process. He admitted that before he began writing each day, he would spend close to an hour penning whatever came out of his head. Just to get the junk out.
This was the writerly equivalent of stretching before a workout. It was also a method of cleansing the distractions from his mind before focusing on a larger project. Within that habit, there's a keen insight.
Imagine you're about to continue work on a story after you finish watching a country music video (the music genre's irrelevant; you'll soon see my point). The images from the video and the lyrics and rhythm of the song leave a residue in your brain. You may even tap your pen in time to the bass line or drum beat. You'll find elements of the music--in everything from its diction to its cadence--infiltrating, even poisoning, your best laid efforts.
It's the effect of recency. The last thing we're exposed to tends to be what we recall best. Or what influences us most. Which is why the 30 minutes or one hour spent jotting your thoughts and distancing yourself from that last song or TV show may help you produce clearer, smarter, untainted prose.