Resources and cost are typically inserted into the activities in a WBS, and summed to create a budget both for summary levels (often called "work packages") and for the whole project or program.
For example, in creating an automobile, an engine, a driveshaft and wheels may all be considered mandatory, whereas cupholders are optional.
Therefore, the fact that the engine, driveshaft and wheels are all mandatory, and each therefore has a value-added of $25,000 does NOT make the value of the automobile $75,000.
The main purpose of the value breakdown structure is to prioritize components and work by the value they are expected to add, and to ensure that the value of the project investment is not reduced by the inclusion of work which has a value-added that is less than its true cost, which is the sum of its resource costs and its drag cost.
If scope is changed during execution, that change should be input into the value breakdown structure, the numerator in computing the Actual DIPP adjusted, and the DIPP Progress Index thus updated.