For project success we need to know if we're on the right path to Done and we need meaningful measures of progress to the plan.
We must measure the increasing maturity of the Deliverables and their Value to the customers in units meaningful to the decision makers - starting with Measures of Effectiveness and Measures of Performance.
We must see Risk coming before they arrive, so we can take corrective or preventive actions to stay on plan.
To see risks coming, we must be able to Estimate both the reducible and irreducible uncertainties that create risk.