[DropkickM16]

It depends on how your API is designed. If it's a tightly coupled RPC-style API or something, this is obviously a bad idea because you'll break every client that didn't see the change coming. But the goal of designing APIs in a hypermedia style is to eliminate this tight coupling and include in each response all the information that a client would need to traverse the application's states. When this is designed properly, it is easier to change the API's functionality without breaking existing clients.

The web is a great example of this (although you may have to squint a bit to see it). Browsers don't need to add additional code or install plugins to handle forms with different fields or links to content of different types, because the semantics of those elements and their interactions are well-defined.