The iterative system helps you find problems quickly because it makes it easy to try it again.

Once a design is completed, problems are noted that many test users had with it. These problems would be quickly fixed through an iteration which should be tested to make sure the "fixes" went through and problems that had occurred are solved. It also finds any new usability problems by the new changed design. Iterative design is specifically aimed to teach you through messing up repetitively until you get it right resulting in a more successful final product.

When applied early in the development stage, significant cost savings are possible.

Iterative testing enables an objective assessment of the project's status. Inconsistencies among requirements, designs, and implementations are detected early.


http://www.useit.com/papers/iterative_design/

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