[randomfool]

In addition to smaller/faster than XML, protobufs make it extremely easy to declare the schema of data, validate data and version your schema. Then the generated wrappers and static type checking in various languages add additional guarantees that you're using the data correctly.

Plain XML still requires a lot to ensure compatibility when it's used across multiple places, protobufs attempt to minimize many sources of the incompatibilities.

Add in a bunch of tools such as protobuf->JSON, protobuf plaintext serialization, etc and it becomes more difficult to argue for using something such as XML or vanilla JSON.

Flatbuffers are still a nice solution for more performance-critical applications.