i.e. only idempotent operations, such as GET. You should not perform a POST using the information obtained in these hints.

Perhaps an alternative analogy is branch prediction? Browser is permitted to run along a particular path of execution because it applies in most cases. But you end up throwing away your work in the case that the prediction turns out to be wrong.

In terms of practical application for this - most modern sites run their content over an additional layer of application logic that runs in the browser e.g. React, or Angular or something. These hints can tell the browser that such-and-such an application framework is required to display the content, and to go get it before the content is available.