Capabilities are immutable and connected to the business or mission strategy. Requirements - technical and operational - that deliver these capabilities can emerge as further understanding emerges. Capabilities are assessed with Measures of Effectiveness, the technical and operational requirements are assessed with Measures of Performance. Technical Performance Measures assure the exit criteria for the work activities (exit from a Work Package, or completion of an iteration in agile) produce the needed outcomes, measured with TPMs, to enable the requirements to be fulfilled, that enable the project to effectively implement the needed Capability.
Knowing the cost to deliver those capabilities provides the business leaders with the needed information to make decisions about priority, sequence and Return on Investment as that understanding emerges.