Ok, so you can "parse" it, which is just a way of saying you can transform a bunch of bytes to a nested structure consisting of a few basic types (dicts, lists, strings, floats, etc). Now what? What can you (or actually your program, not you as a human) do with it without some sort of schema, explicit or implicit?
The REST interface is designed to be efficient for large-
grain hypermedia data transfer, optimizing for the common
case of the Web, but resulting in an interface that is
not optimal for other forms of architectural interaction.
When a link is selected, information needs to be moved
from the location where it is stored to the location
where it will be used by, in most cases, a human reader.
Yes, it's obviously the primary use case, since REST is modeled after HTTP. But the keyword is primary - it doesn't mean it can't or shouldn't be used for machine-driven workflows.