Wireframes are more than a visual or sketch phase, they are a very useful tool to visualize strategies to follow in order to achieve previously defined goals. Wireframes should follow the phase of identification and understanding of the goals and user needs. They are also an essential document for designers and developers in the implementation phase.
In the prototyping phase important decisions are made related to visual design such as visual hierarchy, typographies, colors, images, icons and more. In this phase the proposed functionalities and design can be tested and validated with users and clients prior to moving on to the development phase.
Usability testing is a very important phase to understand how users behave when they try to achieve their goals. It is a great opportunity to improve the efficiency and profitability of products. With usability testing it is possible to gather data to correct usability deficiencies and take decisions that help improving the usability and the profitability of products.