whens the right time to implement circuit breakers? like, when do you actually need em?

you know, i was thinking about system resilience the other day, specifically with microservices. we have some important services that all rely on each other, and i'm kinda nervous about one failure taking down the whole thing. i've heard about circuit breakers for this, but i'm not sure when it's actually the best time to add them. is this just for super high-traffic stuff, or should we think about them for internal services too, even with normal load? what are the main signs that tell you it's time to use this pattern