The observer pattern's primary advantage is promoting loose coupling between the subject (the object being observed) and its observers (the dependent classes). The subject only needs to know that its observers implement a specific interface; it does not need to know about their concrete implementations. This abstraction allows observers to be added, removed, or modified independently without affecting the subject. This decoupling minimizes dependencies and maximizes the flexibility to change or extend the system, which is the core benefit described in the question.

A. tight coupling: This is the opposite of the observer pattern's goal. The pattern is specifically designed to avoid tight coupling, where objects are highly dependent on each other's concrete implementations.

B. cohesion: Cohesion refers to the degree to which elements within a single module are related and work together. While important, it describes an internal characteristic, not the relationship between objects.

C. mediation: Mediation describes the Mediator pattern, where a central object controls the communication between other objects. While it also promotes loose coupling, it is a different pattern, not the term for the advantage itself.

1. Gamma, E., Helm, R., Johnson, R., & Vlissides, J. (1994). Design Patterns: Elements of Reusable Object-Oriented Software. Addison-Wesley. In the chapter on the Observer pattern, under "Consequences," the first benefit listed is: "Abstract coupling between Subject and Observer. All a subject knows is that it has a list of observers, each conforming to the simple interface of the abstract Observer class. The subject doesn't know the concrete class of any observer. Thus the coupling between subjects and observers is abstract and minimal." (p. 298).

2. Freeman, E., Robson, E., Bates, B., & Sierra, K. (2004). Head First Design Patterns. O'Reilly Media. In Chapter 2, "The Observer Pattern," the authors state, "The Observer Pattern provides an object design where subjects and observers are loosely coupled... Because they are loosely coupled, you can add new observers at any time." (p. 57).

3. MIT OpenCourseWare. (2016). 6.005 Software Construction, Spring 2016. Reading 17: GUI Design. Massachusetts Institute of Technology. The reading explains the Model-View-Controller (MVC) pattern, a common application of Observer: "The observer pattern is what keeps the model and view loosely coupled. The model doesn’t know anything about the view, other than that it’s a listener for model events." (Section: "Model-View-Controller").