The waterfall model as well as other conventional standards operates under the assumption that software development is a static process. In real life, a permanent shift of targets and expectations is fact. Agile development methods are using the change as key driver for development. Software is developed in small increments and the customer is regularly invited to redefine, review and confirm the planning.
Agile methods unleash creative resources and promote efficiency and the importance of trust between the customer and the development team. This will save time and money due to agile methods which delivers the right product in the right quality.