What is a key characteristic of Protocol Buffers?

The choice highlighting Protocol Buffers as primarily used for inter-machine communication is accurate due to its efficiency and ability to serialize structured data into a compact binary format. This makes it ideal for communication between services in distributed systems, where quick and efficient data exchange is essential. Protocol Buffers facilitate seamless interaction between different programming languages and systems, allowing for effective data exchange in remote procedure calls (RPCs) and microservices architectures.

The other options do not align with the core characteristics of Protocol Buffers. While it is true that Protocol Buffers can handle telemetry data, the primary intent behind its design is for inter-machine communication rather than a sole focus on telemetry. The claim about being larger and slower than XML contrasts with the fundamental advantage of Protocol Buffers, which is their compactness and speed; they are designed to reduce the amount of data transmitted over the network. Lastly, stating that Protocol Buffers can only serialize unstructured data is inaccurate; they are particularly effective at serializing structured data, allowing for well-defined schemas.