In speaking and writing both, I come up with the best way to express the idea after two or three tries. That means in speaking, I'm apt to 'repeat' myself as I come up with better versions. In writing, I can delete the first attempts...
I have different speaking voices, too, though. I use profanity a whole lot more at home than I do at school, in public forums, and around people who I don't know well enough to know if they find profanity offensive.
I'm a lot filthier on the page, too, than my public persona. But less filthy on page than I am at home...
No one really suspects that the quiet girl with the glasses is rude, crude, and vulgar.