Differences between the Role of Project Managers and a PMO

Differences between the role of project managers and a PMO (Project Management Office) may include the following:
The project manager focuses on the specified project objectives, while the PMO manages major program
scope changes, which may be seen as potential opportunities to better achieve business objectives.
? The project manager controls the assigned project resources to best meet project objectives, while the
PMO optimizes the use of shared organizational resources across all projects.
? The project manager manages the constraints (scope, schedule, cost, quality, etc.) of the individual
projects, while the PMO manages the methodologies, standards, overall risks/opportunities, metrics, and
inter dependencies among projects at the enterprise level.

imparted from Pmbook 5th edition