I would say many of us do not want to use the CPM as if a Swiss Army knife. A knife for job costing, a knife for activity and resource planning, a knife for all record keeping, a unique knife for claim, a knife for payment requests plus a knife to uncork the wine bottle.

Some of these functions are incompatible no matter if you want them to be compatible. Most notably is when used as a tool for payment requests and some minor item is not paid but the successor activity can continue while the remaining portion will be performed after some time. 

Following unit costs per activity can be a real burden as for example you might have brick installation on every floor of a multistory building, why segregating labor and materials under different CPM activities, meaningless without keeping record of the volume of work. Anyone who knows a bit of real unit costing knows quantities are most important and understand that the accounting might happen on a weekly basis for labor while for materials might be latter, after invoices are received and processed. 

BTW Spider Project keeps record of volume of work per period but on a per activity basis and as said before we need the data per "volume of work type" and this is better done by the job costing module.  

I use volume of work for modeling purposes, for the software to adjust activity durations based on remaining volumes of work.  We plan as our Project Managers would do it on the field, we assign variable resource quantities to activities so that if 20 units are needed but 15 are available and it is enough for activity execution the activity will not be delayed until 20 are available, will start earlier at a slower pace until the 20 are available, the duration might increase but the finish date will be earlier, volume of work is necessary to model this every day scenario on our jobs. 

For impact and claims it might be you are required software different to what you have already integrated with your financial system. Even having CPM integrated to financial system is rare and pretending to force all to use it is wrong.  I would say CPM data can be easily manipulated while payroll and other accounting records are not as easily manipulated, why downgrade the accountability?

Trends do matter quite much but for many of us resource productivity trends are easier to follow using the job costing module that pulls down the data from other modules such as time cards, payroll, account payable, purchase order ... 

CPM/PDM when used as a single tool for every purpose is no match to using CPM/PDM along with the many tools available to management. CPM/PDM is another source of information useful for management but not the only one.  The most important of all tools I consider are the brains of the management team.