Sentry.io has been using browser profiling to collect over 2M profiles and gain insights into how its users experience its dashboard, revealing issues such as UI jank that were causing slow interactions for users. Profiling helps developers proactively identify performance issues without relying on customers to report slow behavior, enabling them to get ahead of performance problems. By analyzing the most commonly collected spans during page-load events, Sentry identified a UI long task event span with a high frequency and p75 time, which was causing jank due to inefficient code in React tree diffing. The team used profiling data to pinpoint the issue, analyze the source code, and implement a solution that mitigated the problem, resulting in improved runtime performance for users.