I would argue that paper prototyping for interface design has a very limited use. Modern digital tools for prototyping, if used right, can get you to the desired result faster and welcome frequent iteration.
Changing something on a hand-drawn paper prototype (especially the ‘interactive’ kind) would mean redrawing the whole thing more or less. And as soon as designer’s tools start limiting them, I see a problem.
Sometimes digital can be best for quick and dirty.
More important though is being ready to iterate a lot when you’re at the start of the project and be ready to kill your darlings.