One of the biggest challenges when designing a new product (or significant revision to existing product) is to get everyone else in the company behind you and the project. A sure way to do that is to build out (in prototype form) the most visible, core functional areas that are ever-present in the product, like the main navigation and branded panels (ie, the chrome) to make it really seem like it’s coming alive. PM’s, VP’s, Directors, Leads from other departments can connect to that easily. Else it’s just pretty pictures all disconnected from separate prototype pages/components that lack coherence, too random, not congealing…gotta make it “real” as THE THING TO BE for all to look upon and point to.