In my experience most projects don't have a real project sponsor. A project sponsor is the senior manager or executive that champions the project in the organization. The sponsor provides support for obtaining resources, provides strategic direction, and acts as the decision point for questions outside of the project manager’s authority.
Every project that crosses functional lines of authority needs a project sponsor to remove barriers, assist in resolving conflict, and mediate negotiations. The sponsor can also act as a mentor and coach to the project manager and team members.
The project sponsor is usually chosen by senior management, but sometimes the sponsor volunteers because the project directly impacts their resources or budget the most.
Typically Project Sponsors are responsible for:
Providing project direction
Monitoring project progress
Assisting the Project Manager to define the Project Management process for the project
Approving final scope, project objectives, schedule, resource assignments, roles and responsibilities
Providing accurate, relevant and timely communications in writing when appropriate
Approve scope changes
Obtain or resolve issues surrounding resources (people, money, equipment)
Setting project priorities and removing barriers to project success