api gateway vs direct service calls which to pick

hey everyone, i've been thinking a lot about how we structure our microservice interactions. we currently use an api gateway for most external traffic, which handles auth, rate limiting, and request routing. but for internal service-to-service communication, we mostly bypass the gateway and call services directly. that seems efficient, but i'm wondering if there are scenarios where routing internal traffic through the gateway, or using a dedicated service mesh, would be more beneficial. what are your thoughts on the trade-offs? when do you opt for direct calls, and when do you prefer an intermediary like an api gateway or service mesh for internal communications