[lmm]

It's a lot higher-performance, because you virtually don't have to parse. Remember when MySQL started supporting the memcached protocol because it'd reached the point where form simple pkey lookups it was spending more time parsing an SQL query than actually executing it? It's like doing that for your program.

But for me at least, the real advantage over JSON isn't the performance but the schema compatibility. You have a spec for your data and generate code from that, which means the spec is guaranteed to be correct, and there's clear documentation about what changes to the spec are or aren't forward or backward compatibile. (You get the same thing from the original Protocol Buffers though).