А именно вот этот абзац в статье получается фигня, или я ее не правильно понимаю?
“When more experienced developers look at the code they write, they consider how it fits into the project they are working on. The implementation of a method is only part of the solution. Should it be possible for ViewController subclasses to override the fetchNotes() method? If the answer is no, then you should attach the private or fileprivate keyword. This not only makes sense in the context of access control, it also improves performance. Why is that?
When the compiler inspects the fetchNotes() method, it realizes that it is declared as private, implying that the method cannot be overridden by subclasses. The compiler picks up this clue and safely infers final on the method declaration. Whenever the final keyword is attached to a method declaration, calls to that method can be dispatched statically instead of dynamically, resulting in a tiny performance gain.”