Mockups are more than just a step between wireframes and prototypes. In fact, even this transitional function can vary in importance and implementation. At times mockups are helpful to support creative and brand standards, getting stakeholder buy-in, or demonstrating a high-fidelity design of wireframe. Other times mockups help to demonstrate standardized elements of the product.
I often draw mockups in Photoshop and display them through a design communication and collaboration tools like Invision App and ConceptShare for revisioning, feedback and proofing.View Portfolio