If you stand on a street corner or walk down the grocery aisle and talk to yourself, people might think you're a little touched. That's certainly what I thought about a woman a few years ago when I saw her apparently chatting with a display of sirloin steaks--that hands-free Bluetooth device of hers sure had me fooled.
Chances are, most of us talk to ourselves now and then, and we just sorta keep it low-key and not too public. But if you're a writer, you should talk to yourself now and then. Read with your lips and your larynx to hear and feel the flow of your words. No, no, don't read newspapers or books that way, just the drafts of your own work. You'll find those double words and repeated sentences, the phrasing that doesn't sound quite right. Maybe you'll spot a passive voice or an incomplete sentence.
The point is to use more than just your sense of sight. Use your sense of hearing as well, and you will pick up on those errors that might otherwise slide right past you.
Right now I'm typing with the office door closed, so my wife doesn't hear me talking to myself.