Sentry's mobile error monitoring provides real-time visibility into how fast an app starts, the duration of HTTP requests, and other performance metrics such as slow and frozen frames. The four key metrics every mobile team should track are cold starts, warm starts, slow frames, and frozen frames, which can help identify bottlenecks and speed up apps. Sentry's auto-instrumentation allows developers to easily monitor their app's performance without additional setup or accumulating testing devices, providing detailed insights into transactions, spans, and Mobile Vitals. By tracking these metrics, developers can prioritize critical performance issues, trace the issue down to the root cause, and solve them faster, ultimately providing a delightful user experience.