So, when should you use API Gateway and when should you just call services directly?

hey everyone, im trying to wrap my head around when an api gateway really makes sense versus just having clients call microservices directly. were building out a new system and debating this. my initial thought is a gateway is good for auth, rate limiting, and simplifying the clients view, but it adds another hop. for simpler internal services, maybe direct calls are fine? whats your experience? when did you decide to introduce a gateway, and what were the tipping points?