Adults acting like children
Apparently, the use of a short time for the exercise removes one's need for perfection, and the use of Crayons "encourages adults to act like children in all the right ways, instead of acting like children in all the wrong ways." So says Janice Fraser.
The end result is that one solicits ideas from involved parties and gets the differences about a product out of people's heads and into the open. The end result is hopefully that the disparate ideas must be reconciled early in the process in order for the product to proceed.