In a post to his site today Ben Ramsey shares his response to a question about hypermedia in APIs and how they could make the API more brittle if used incorrectly.
One of the most common problems I see in API development is lack of hypermedia, or none at all. By hypermedia, I mean links that describe relationships among data in the API. When hypermedia isn’t used, the API becomes brittle, and those building clients that talk to the API are forced to code to URLs. The URLs become an important interface to the API, and if they change, they break everything. This leads to URL-based versioning schemes, and the only upgrade path for clients is to modify their code to accommodate the new versions.
He suggests that when APIs use hypermedia they tend to no longer rely on the URLs of the resources (as they're linked from the meta in other requests). He also shares the slides for a presentation he gave at this year's True North PHP Conference with more information on the topic.