I consider productivity [production rates] trends as the most important metric to follow on a Project.
Cost and effort are directly related to productivity, therefore it is a must on all Projects to follow and record cost [money] and effort [hours] versus production [volume of work]. Job costing can provide for this but it is not good enough with the time element, it is the relation with time element forecast that CPM models handle very well.
Project Managers are always keeping track of cost per unit of work as well as production rates, this have been for decades, perhaps centuries before CPM. My guess is that the builder of the Great Pyramid would continuously follow up on how many stones were installed on any given day and by how many men.
Once your project starts running it is that real CPM work starts, you shall gather the required statistics preferably using your software and use these to forecast trends also preferably using your software. Perhaps this is the most essential procedure managers must perform in order to manage the work.
Productivity, productivity, productivity ...