Introduction - Paper Prototyping: The Fast and Easy Way to Define and Refine User Interfaces - page 8

Benefits of Paper Prototyping
Here's a preview of paper prototyping's advantages:
Provides substantive user feedback early in the development process—before you've invested
effort in implementation.
Promotes rapid iterative development. You can experiment with many ideas rather than betting the
farm on just one.
Facilitates communication within the development team and between the development team and
customers.
Does not require any technical skills, so a multidisciplinary team can work together.
Encourages creativity in the product development process.
Someone once asked me what the paper prototyping "bumper sticker" would say, and my answer was,
"Maximum Feedback for Minimum Effort." That's really what it boils down to—an efficient means of
getting make-it-or-break-it information about your interface. Using only a few office supplies and a dash
of ingenuity, you can get all sorts of useful feedback in time to do something about it before the next
release.
Of course, no technique is perfect, and this includes paper prototyping. One important drawback is
paper prototyping's difficulty in detecting some classes of problems. In addition, depending on the
circumstances of the project, there are cases in which the benefits of paper simply aren't very
compelling.