Prototyping

Prototyping helps to:

• Explore different ways to navigate
  through a system to accomplish tasks.
• Identify major problems
  in using the system.
• Support metric-based evaluations
  of the system's design and ROI of its usability.
• Communicate system attributes and specifications
  to the design and development teams.
• Determine the user-friendliness
  of the system before it is built.

Prototyping helps to avoid:

• Errors
   in workflow, data design, navigation, usability, and code itself. These can be avoided entirely by creating a solid prototype.
• Changes
  that are extremely costly, particularly those after development is complete.

Applications or web sites are usually prototyped to conduct usability testing, an objective way of obtaining user feedback.

Prototyping Offers Big Savings

Jacob Nielsen (2003) reports that paper prototypes save money:

Ten times the impact if you discover a needed design change early, and 100 times cheaper to make the change.