When should you move from REST to gRPC?

hey everyone, i've been thinking about microservice communication patterns lately. we're currently using REST/JSON for most of our internal APIs, and it's been working fine. however, i'm starting to wonder if there's a point where the overhead of JSON serialization/deserialization and the HTTP/1.1 connection management becomes a bottleneck or adds unnecessary latency. when have you found it beneficial to switch from REST to something like gRPC with Protocol Buffers? what were the primary drivers for that decision? looking for real-world experiences and advice on when this migration makes sense.