so, when's the best time to put in a circuit breaker

Hey everyone, I've been thinking a lot about distributed systems lately, and specifically about how to handle failures gracefully. We've all seen those cascading failures where one failing service brings down others. A circuit breaker pattern seems like a solid solution to prevent that. But I'm curious about the tipping point. At what scale or complexity do you guys find yourselves reaching for a circuit breaker? Are there specific metrics or failure rates that signal it's time? What are your experiences with implementing them, and what trade-offs did you encounter?