The main benefit of User-Interface Prototyping per se is that it reduces the risk of developing an unacceptable user interface and having to rework it later. Beyond that, the benefits of User-Interface Prototyping depend on whether you use Throwaway Prototyping or Evolutionary Prototyping.

In case studies, Evolutionary Prototyping has decreased development effort dramatically, from 45 to 80 percent (Gordon and Bieman 1995). On the other hand, Throwaway Prototyping is more a risk-reduction practice than an out-and-out timesaving practice. It helps keep schedules under control more than it helps reduce them.