It might be appropriate to use gRPC in a microservices architecture in situations where improved performance, efficiency, and reliability are important. 

For example, if an application needs to make multiple inter-service communication calls in order to get the data that it needs, using gRPC can reduce the network overhead and improve the overall performance of the system. 

Additionally, if an application needs to be able to communicate between microservices using a strongly typed interface description language, using gRPC can provide the efficiency and reliability needed. 

https://learn.microsoft.com/en-us/archive/msdn-magazine/2019/october/cutting-edge-using-grpc-in-a-microservice-architecture