The principle benefit is that you can use the schema to define the data format, which means you can pack the data in more tightly (you don't need a byte to say "this is an object" if you know that the input data must be an object at this point). That's a big benefit in certain situations, but if you're using this sort of stuff just to get validation then you're probably better off using JSON Schema and having a wire transfer format that you can read easily without additional tools.