api gateway versus calling services straight up

hey folks im wrestling w a common microservices decision and wanted to get your thoughts. for internal service to service communication, when do you lean towards using an API Gateway as the sole entry point, versus allowing services to call each other directly? i know gateways offer centralized auth, rate limiting, and request aggregation, but direct calls can sometimes feel simpler for smaller setups or when latency is super critical. whats your experience here? when did you decide one way or the other, and what were the biggest drivers