In a project, many people work together, contributing effort towards the success of the project. Without someone assuming the role of the project sponsor, the project would suffer by wasting time and resources. 

The project sponsor champions the project at the highest, most senior level of the company or business. He has the business authority to make choices and commit the financial resources and other resources required for the project. Part of the sponsor's purpose is to clear the project of any organizational barriers. A sponsor supports the project's cost and benefits.

There is a distinction between the position of the sponsor and the project manager's role. The sponsor gives the project manager the authority and responsibility for carrying out the project work while also maintaining a level of control. A sponsor supports the project and protects it from unnecessary changes as long as the project continues to reach the organization's strategic objectives. A solid sponsor should have the clout to interact with the CEO and key stakeholders adequately. He can approve or reject project outcomes. He also claims a certain amount of responsibility for the project's performance. 

What does a project sponsor do?

Below is a summarized list of the sponsor's duties during every project management process. You can reference this list in Rita Mulcahy's CAPM Exam Prep book Fourth Edition:

During or before project initiating, the sponsor:

• Has requirements that must be met

• Is a project stakeholder

• Participates in developing the business case for the project

• Helps define the measurable project objectives

• Advocates for or champions the project, especially while the project concept is being put together

• Serves as a voice of the project or spokesperson to those who do not know about the project, including upper management

• Gathers the appropriate support for the project

• Ensures buy-in throughout the organization

• Provides funding

• Provides high-level requirements

• Provides information regarding the initial scope of the project

• May dictate milestones, key events or the project end date (along with the customer)

• Determines the priorities between constraints (if not done by the customer)

• Provides information that helps develop the project charter

• Give the project manager authority as outlined in the project charter

• Sets priorities between projects

• Encourages the finalization of high-level requirements and scope by the stakeholders

• Guides the process to get the project approved and formalized, assisted by the project manager as necessary

During project planning, the sponsor:

• Provides the project team with time to plan

• May review the WBS

• Identifies risk

• Determines the reports needed by management to oversee the project

• Provides expert judgment

• Helps evaluate trade-offs during crashing, fast tracking, and reestimating

• Approves the final project management plan

During project executing and project monitoring and controlling, the sponsor:

• Supports the efforts of the project manager

• Protects the project from outside influences and changes

• Enforces quality policies

• Provides expert judgment

• Helps evaluate trade-offs during crashing, fast tracking, and reestimating

• Resolves conflicts that extend beyond the project manager's control

• Approves, rejects, or defers changes, or authorizes a change control board to do so

• May direct that a quality review be performed

• Clarifies scope questions

• Works with the project manager to monitor progress

During project closing, the sponsor:

• Provides formal acceptance of the deliverables (if they are the customer)

• Enables an efficient and integrated transfer of deliverables to the customer

• Supports the collection of historical records from the project

References:

Rita Mulcahy's CAPM Exam Prep: Rita's Course in a Book for Passing the Certified Associate in Project Management (CAPM) Exam, by Rita Mulcahy and Rita Mulcahy, RMC Publications, 2018.