[pavlov]

In practice it often does, because introducing brand new patterns alongside existing ones may be frowned upon in a large project.

Consider a codebase that uses the "comment indicates ownership transfer" pattern everywhere. Would it improve the code quality if one developer suddenly introduced unique_ptr, std::move and rvalue references in just one place in the API, when every other call would still be using the old style?

To my taste, the mental overhead of having two different ownership patterns would outweigh the advantage of the new compiler checks (which in this case would be mostly theoretical, since the devs working on this project would presumably feel at home with the old pattern).