The idea behind rapid writing is to turn off your editor. Write messy. Write so that your words spill onto the page as fast as your thoughts. This is also referred to as stream of conscious. There is no form. You can punctuate … or … not. You can add dashes, dots and leave grammar to the wayside.
Rapid Writing allows you to jump around, just like the thoughts in your head. You can repeat yourself or completely shift gears.
The purpose here is to get your pen scratching across the page from the words and ideas that roll through your brain.