In what cases will this be better than REST + Protobuffs (or similar shared-model backed binary encodings)? Whenever I've started thinking I should design a ne

In what cases will this be better than REST + Protobuffs (or similar shared-model backed binary encodings)? Whenever I've started thinking I should design a new TCP or other protocol to address a problem, I've consistently ended up concluding it'd be going in the wrong direction- unnecessarily low-level in a way that doesn't contribute to getting anything useful / meaningful done. Could just be me :). I'm sure there are valid use-cases, just not clear to me how often this is the case in real life. Could this be useful for creating a new rust bittorrent implementation?