Explanation
According to the System Demo article on the Scaled Agile Framework website, objective milestones, like the System Demo, are useful because they provide tangible evidence of progress and allow for cost-effective adjustments towards an optimum solution. The article states that "The system demo offers the ART a fact-based measure of current, system-level progress within the PI. It's the true measure of ART velocity and progress. Achieving this requires implementing the scalable engineering practices necessary to support Continuous Integration across the ART." The article also states that "The system demo provides the opportunity to get fast feedback from the stakeholders, which is essential for building the right solution. The feedback can be used to validate assumptions, evaluate hypotheses, and identify potential pivots or changes in direction. The system demo also helps to identify and resolve any integration issues, dependencies, or risks that may affect the solution's fitness for purpose or compliance." Therefore, the correct answers are D, they provide tangible evidence of progress, and E, they allow for cost-effective adjustments towards an optimum solution. The other options are not accurate, as they are not the reasons why objective milestones are useful.
They do not necessarily allow the contracting officer to release funds for payment, satisfy phase-gate governance processes, or satisfy a SAFe requirement.