Sentry Performance` helped identify performance issues with their `Flagr` feature flag system by using its auto-instrumentation and manual instrumentation capabilities to pinpoint slow code paths, specifically the deserialization of large JSON responses, which was taking a significant amount of time. By identifying this issue, Sentry was able to optimize their implementation, reducing the time it took to check all 50 feature flags from 900ms to 10ms. The use of `Feature Flags` is a great tool for controlling system behavior without destabilizing the codebase, but having the right tools and insights, such as those provided by `Sentry Performance`, is crucial to using them effectively.