What is the role of Project Management Office

Strategic planning and governance
The strategic selection of potential projects can be done according to the business goals of the organization. PMOs then advise senior management or C-level leaders to select candidate projects that best align with the strategic goals of the company, by providing a sound business case and a clear cost/benefit ratio.

Best practices and process
PMOs implement and consolidate best practices and processes within the organization. 

Common language, culture and mindset
A PMO helps disseminate a common project culture and mindset by informing, communicating and training employees about different techniques, methodologies and best practices in the industry.