What does a Project Manager Do?

There's lots of discussion of late about the role of a Project Manager. Whether a Project Manager is needed in the agile world. Whether a Project Manager and Project Management is really a "directorial" role or a "coaching, personal guide?"
    Here's a clear and concise definition I found while preparing for this weeks project management performance reviews on one of our NASA programs

The primary function of project management is to ensure that the project is implemented to meet the established budget, schedule, safety, and performance requirements to satisfy its objectives.

It takes an organized team to fulfill this function.