The essence of sketching is selectivity. With forward sketching you rough out some issues in code you are about to write, usually discussing them with a group of people with your team. Your aim is to use the sketches to help communicate ideas and alternatives about what you're about to do. You don't talk about all the code you are going to work on, just important issues that you want to run past your colleagues first, or sections of the design that you want to visualize before you begin programming.
via martinfowler.com