Microsoft.Xna.Framework.Game class has a Services property that allows the programmer to add a service to their game by providing the type of the class and an instance of the class to the Add method.
Now, instead of having to pass an
AudioComponent to all classes and methods that require it, instead you just pass your
Game instance and look up the service. (Service Locator)
Now, because games have many services (GraphicsDevice, SceneGraph, AudioComponent, EffectsManager, et cetera), you will now basically be passing Game to everything.
So why not just make these instances a Singleton? Well, because Singletons are bad because they have a global state, prevent testing, and make your design much more brittle. Service locators are equally considered to be an anti-pattern to many because instead of just passing the dependency to an object, you pass a service locator (the Game) which couples that class with the rest of the services.
So then why are Services recommended in XNA and game development? Is it because games are different from regular programs and are highly intertwined with their components and having to pass every component necessary for the functioning of a class would be highly cumbersome? Are Game Services just then a necessary evil in game design? Are there alternatives that don't involve lengthy parameter lists and coupling?