Mockups are the glue that binds the wireframing and prototyping stages together. While the mockup furthers the wireframe’s purpose of documentation and organizing the team’s vision, it has an extra advantage that the wireframe does not: with its superior visuals, making the mockup is more useful to stakeholders and investors. And while screen mockups aren’t interactive, an experienced app or web investor will be able to glean some functionality just by examining a visually faithful one.