[extension]

The important quality that HATEOAS gives you is the freedom to evolve the application on the server without changing the client. It's the reason that the web can be used for things that TBL didn't anticipate when he invented it. If an API can't adopt new functionality without breaking clients then there is no sense in calling it RESTful.

As other commenters, and Fielding himself, have pointed out, REST is inefficient in terms of both computer and human resources. It's an architecture optimized for wide scale and long term use. That's why most APIs don't turn out very RESTful.