The importance of performance in user experience cannot be overstated, as it directly impacts how users interact with an application. Measuring and optimizing performance is crucial to delivering a good user experience. Developers have the power to affect UX by focusing on user-centric metrics such as largest contentful paint, which measures the time from when a user navigates to a page until the largest image or block of content loads. Partitioning data by device, region, product, and user journey can help identify areas where performance may vary, allowing for targeted optimization efforts. By focusing on these key metrics and taking action to improve them, developers can maximize returns on site design and navigation, ultimately driving better user engagement and experiences.