Serialization and deserialization efficiency is specially important for mobile apps, in which the CPU used to parse/serialize JSON (or gzipped JSON) can become very prominent.

Apache Thrift, IIRC, is actually a reimplementation of protos, in the same way that Facebook's Buck is of Google's Bazel.

I have some times looked at "raw" binary protos to inspect the string fields, that happen(ed?) to be byte-aligned and so readable in a text editor. Not sure off the top of my head if that's always the case.