If you want to have a set of globally defined types and/or language-independent types to share between your various programs or services, gRPC and Protobufs are a good option.
Also, anywhere that you might use RPC you could use gRPC. It has a compact wire format and is pretty user-friendly as far as designing your RPC req/rep types.
I used gRPC for numerous hobby projects during my undergrad to glue together binaries running in different languages (e.g. a simulation server running in C++ and a scripting client in Python). By passing around a shared data structure (Protobufs), one does not need to waste time writing serialization/de-serialization adapters. It is also useful for gluing together microservices.
FB's Thrift also solves the same problem, and is an alternative to gRPC.
Going into the microservice aspect above, it provides a nice abstraction of remote function calls, so that you can write microservice code that looks like it's executing a local function, but is really just expecting a remote server to implement the method name. In general, that's just RPC calls though. Google's implementation has proven very intuitive to learn, and has a nice size community online for help debugging, etc.
Latency-sensitive / chatty microservices can benefit greatly. Some of this is by nature of http2 but it’s extended by protocol buffer packaging of messages and other client smarts. Inter-service comms is where this popped onto my radar recently.
You get type safety in your API, you get autogenerated client code, and you get http2 out of the box.
Personally I find the autogenerated client code to be the biggest upside. Anyone who wants to use your API, in any language supported by the RPC, can start doing it with very little work. Gone are the days of maintaining officially-supported client libraries.
I'd more say that it gets rid of the need for officially-supported client libraries, but such libraries can still be a nice convenience for idiomatically mapping your service's higher-level concepts to what makes sense for a given language.
Still, it's a big win to automatically make your API available in all gRPC-supported languages, since most companies can't justify the business cost of a hand-crafted library in even one of those languages, let alone all.
