Subclassing Scenes Versus Assigning a Delegate
Use a scene delegate to share app logic across various scenes.
Overview
Often, your app subclasses SKScene to deliver gameplay. Your subclass usually:
Lays out initial scene content
Defines app logic that runs every frame
Implements responder methods to handle keyboard, mouse, or touch events
An alternative pattern is to assign a delegate that handles SKScene instead. For example, if you make the view controller the delegate for your scene, it can use multiple scenes that share the same SKSceneDelegate implementations. The view controller participates in event handling and so it can respond to user input also.