I talk to myself a lot when I write, especially when I write dialogue. It mostly helps me avoid the trap of using dialogue to move the plot along, like this:
"Come with me, Matilda, and don't ask any questions, even though I know this is very sudden and I haven't given you any reason to drop the important thing you're doing."
Fortunately (or unfortunately) my main characters tend to resist that sort of thing.
"Come with me, Matilda, right away."
"Ohh, do I have to? I'm in the middle of cooking dinner."
*Sigh* "Are you really going to make me summarize the plot up until now just to get you into your front yard?"
The pitfall of talking dialogue out loud is that I'm a lazy, slang loving talker. I grew up in the suburbs of New York City, I lived for almost a decade in Virginia, and now I live near the Great Lakes. I have no problem dropping a sentence like, "Y'all guys gonna want some pop?"
The problem with writing sentences like that is, unlike speaking them, the words that stand out the most are the ones written with unusual syntax. Y'all and gonna seem like the most important words in that sentence when written down, or at least the most noticeable.
When critiquing and reading, I see people use gonna, wanna, and 'cause as shorthand for "typical kid." But I think of them as typical Brooklyn/Queens blue-collar words. Which do you imagine Archie Bunker saying?
1. I am going to get to that.
2. I'm gonna get to that there.
If he were from Upstate New York, he'd add the introductory yeah: "Yeah, I'm gonna get to that." And if he were from Virginia, the verb would be complex: "I'll be getting to that."
So what happens for my novel set in blue-collar Long Island? Every character can't say "gonna" all the time just because they would in real life. It would irritate the reader. Plus people from different regions would wonder why the adults say "gonna." (Well, where do they think kids pick it up from, English class?) If I pick one character and make it his or her distinctive characteristic, what's the criteria? Intelligence? That would be condescending. Time lived in Brooklyn? Then the adults would say gonna and not the kids.
So now when I'm tempted to use "gonna" just because I say it, I remember the immortal words of Principal Skinner:
Bart: "I was gonna!"
Principal Skinner: "Gonna, shunna, wonna."
... and try to use variations like gonna as sparingly as possible.
-- Kate, Miss Perfecting the Pages