It is mostly *different* information---less than the book in total, but a very nice addition. That's what I think of it as: you buy the book, and then if you want the "extended dance remix", you get the website too.
The other role it can play is that if you have a slightly out-of-date version of UG, the website will give you access to the most recent published plans for a smaller price. (Then again, my copies never last more than a year or two, so I can't imagine not replacing it at least semi-annually!)
The thing I like about the website is that it has many many "special situation" touring plans. For example, most people shudder in horror at the thought of always arriving at the Magic Kingdom hours after rope-drop, but if that's you, there's a touring plan for you. If you have only young princess fanatics, there's one there too.