I wouldn't say that binary formats are more faster to process. If you have a look at CSV or fixed-field-length textual format - it is still can be processed fast.
I would say, everything depends on who is the consumer. If the human being is at the end (like for HTTP or RSS), then there is no need to somehow compact the data, except maybe compressing it.
Binary protocols need parsers/convertors, difficult to extend and keep the backward compatibility. The higher you go in protocol stack, the more human-oriented protocols are (TCP is binary, as packets have to be processed by routers at high speed, but XML is more human-friendly).
I think, size variations does not matter today a lot. For your example, hello
will take the same amount in binary format as in text format, because text format is also "binary" for the computer - only the way we interprete the data matters.