Consider the impact of project decisions on enterprise value, not just project or PMO objectives.
If the PMO has separate objectives to the ‘project’ or the enterprise value, the PMO is out of control.
A good PMO is a facilitating mechanism to give order and uniformity of process and language to projects, assist in coordination of resourcing, sometimes including financial resources (cash flow, finance needs), communicate overall project commitments to the executive and identify emerging deviations from plan. These need to be first taken up with the PM (or even he/she is not ‘empowered.) and jointly taken to the project executive group (the governing body for the PMO).
The PM has to balance the investment-value couple: the outturn value has to be over the investment hurdle: will the return be enough? Almost no other question applies.