Allow easy storage and portability of data across scenes
There's 2 goals here. The first is making a prototype seem more real to the User and the second is communicating the prototype to Developers perhaps in another country.
For Users, being able to log in and see your name across the site is more realistic, or adding elements to a to-do list and seeing them appear. For developers, especially off-shore, they need some idea of how the data actually works rather than an abstracted story. If you're in Asia there's often so much context missing they can't imagine what you're saying, even with a story, so conveying more detail is key.
The solution? Why not add a Prototype Data Source where you create data 'buckets' rather than messing about with silly variables like in Axure. And JustInMind's data implementation is waaay to complicated.
Thanks, Markus. Totally agree.
I'd have to say I use Axure's variable values all the time and I find that a perfectly good way to persist data across screens...