[mr_crankypants]

I find that the human benefits of using something like protobuf outweigh the human benefits of using JSON. The machine benefits are just a cherry on top.

Protobuf - or, more specifically, proto files - gives you a central place where you can define and also document your formats. You can throw an ASCII-field UML sequence diagram in there, if you need to. And it's right there in the single file that everyone will use to communicate the protocol, and the protocol at least can't change in any structural way without editing that file, so it's got a much higher chance of being kept up-to-date, and of being read by the people who need to read it, than any of the available options for documenting JSON-based protocols.

All JSON gives you is human readability, and browsers can read it without a library. The 2nd, I don't care about with back-end services. The 1st I don't really care about at all, because command-line utilities and library functions for dumping protobuf datagrams to a text format are a dime a dozen.