Requirements Inception 

Requirements management

Requirements validation

All of these

A prototype helps in development of accurate project schedule.

 A working prototype helps the customer to provide meaningful feedback about the requirements.

A prototype is iteratively enhanced into a working software and is finally deployed at the client site.

A prototype is deployed at the client site as an operational software till the full version is developed

Estimating software development effort and cost

Planning software testing activities

Managing software risks

Predicting software defects