Rex,

Indexes on Views are necessary to take advantage of Rushmore Optimization.
According to the latest MM Dev Guide ver 4.1 (pg98):

Step 2:Creating Views
Rushmore Optimization

Make sure that the view is optimized for Rushmore. This means not only creating indexes for your primary keys but also for every field listed in the Selection Criteria page.


This could be crucial in situations where you are handling large tables

Regards,
Ed Chin