User personas play a crucial role in UX/UI design by representing different segments of the target audience. These detailed profiles help designers understand users' needs, behaviors, and motivations, enabling them to create tailored experiences that resonate with various user groups. By considering user personas, design teams can make informed decisions about features, layouts, and interactions that enhance usability and satisfaction. This approach fosters empathy within the team, ensuring that the final product aligns with user expectations and improves overall engagement.