EventDispatcher aides you in event-driven development. In event-driven developement you are using events (or often referred to as notifications) to build a flexible communication between different objects and components of oyur application.

Objects may register themselves or any kind of event-listener to a specific type of event (e.g. a successful login by a user). Other objects will then send a notification when any event occured and attach some additional information (the context of the event) to the notification.

So you could think of event-driven development as an advanced subject-observer-pattern.