Together with its more famous brother "Iterator", they are currently the two only implementations of the "Traversable" interface, which is needed for objects so they can be used within a standard foreach() loop. But why and when should we use the iteratorAggregate?
He answers his question with an example - a book that contains chapters. With a normal iterator you'd have to define standard functions (like valid, rewind or key). Using the IteratorAggregate you can push items into an internal array (like chapters in a book) and call a "getIterator" method to get this set. He also takes it one step further and shows implementing the "Count" interface to make it easier to get a total count of the items in the iterator. Sample code is included to help clarify.