Highly practical. More than just making the design process much more conducive to iteration, you also have a designer doing the implementation. This is great,

Highly practical. More than just making the design process much more conducive to iteration, you also have a designer doing the implementation. This is great, because it means that you no longer have to explain that a certain design treatment can't be done in code. Moreover, if there's a problem with the experience of using a certain element, the designer can change it on the fly with little overhead.