It doesn't seem to be a very well documented/advertised feature, at least from what I've seen! I almost didn't get the EX version because animation frames was the main difference I could see, too--but I'm glad I took the plunge! I've really liked having the ability to save a set of pages together and edit the text for all of them at once.
Here's a screenshot of the Christmas special I'm working on right now; the set of 5 pages saved as a "story" on the left (I can click the thumbnail to open and edit the page in a new tab) and the story editor on the right: