When should you think about using an API Gateway?

i've been thinking about when it's the right time to introduce an api gateway into a system. we're currently managing our apis directly on our services, but as we grow, i'm seeing the need for centralized concerns like authentication, rate limiting, and request/response transformation. have others found a tipping point where the benefits of a gateway start to outweigh the added complexity and potential single point of failure. what are your experiences with implementing an api gateway