Yes, with fairly simple applications, websites, and various other design/mockup uses you can skip this step. It’s really not required until you get into applications that have multiple pages and/or pages that interact with each other. Once you get into the realm of an application that switches content based on user interaction, it’s impossible to predict all the correct placements and information.
Let’s phrase it a better way, can you tell me what happens after you click around on the application/website 14 times? No? That’s what a mockup or graphical design provides.