Schemas save you space, but then you lose the ability to understand the data without the schema. That's where JSON has always been handy despite its inefficiencies.
Of course you can get the same kind of thing in binary. I wrote a drop-in binary JSON replacement because it's easy to write a binary one that's twice as fast as simjson and yyjson. The important thing is to never give the drop-in replacement any extras that break roundtrip compatibility.
Was a fun little project to write, and quite useful for me: https://github.com/kstenerud/bonjson