It is useful if you are able to generate code from it. I know one big software company (more than 3000 employee) that generate 90% of all it's code base (~20M lines of code).
Must be some pretty trivial software, since 90% of the code base is apparently class and function declarations filled with empty or pointless (get/set) OO garbage.
Some enterprise software, most of the patterns are well know and the customization point are well defined.
I would describe more as a well know domain with clear constraints than trivial software.
They generate a lot of code also for high critical real time software (avionics and space) but that is not really trivial.
I'm skeptical the code generators are used for the actual function bodies at any level. That's 90% of any non-trivial code, not function and class declarations and stubs.
I wonder how that company pulled this one off. In my experience, UML diagrams end up either too shallow to be useful for code generation, or so dense that they're totally useless for communication with non-technical stakeholders.
I don't know the details so I couldn't say. I was surprised as well to be honest. I talked briefly with one of the owners, he did know quite in a deep way what he was talking about. A lot of emphasis for the process, using new technologies but without the 'madness' that we see usually in the Javascript world.