Authorization Header matters because API bugs are often contract, status, header, authentication, or network-boundary bugs rather than UI bugs. It gives builders a precise word for the thing they are changing, debugging, reviewing, or shipping.
ELI5
Think of Authorization Header as a message rule for how apps talk to each other. It gives one small job a clear name so the whole app is easier to understand.
In practice
Use it when a browser, backend, agent, payment provider, or external tool needs to exchange data reliably. In practice, name the owner, input, output, failure mode, and proof before relying on Authorization Header.