Usability testing plays a crucial role in UI design as it helps identify usability issues, assess user satisfaction, and improve overall user experience. It allows designers to gather feedback directly from users, uncovering insights into how well the interface performs, how intuitive it is, and if it meets user needs. Usability testing helps validate design decisions, identify pain points, and optimize workflows. It helps designers understand user behavior, preferences, and expectations, leading to more effective and user-centered designs. By detecting and addressing usability issues early in the design process, usability testing helps enhance product usability, increase user engagement, and ultimately, drive user satisfaction and business success.