In PRINCE2, the role responsible for appointing the Senior User, as well as other key project roles such as the Executive and the Senior Supplier, is typically taken by someone from corporate or program management, or the customer. This aligns with the principle of clearly defined roles and responsibilities, ensuring that the project has clear governance and accountability. The Senior User is appointed to represent the interests of all those who will use the project's products, who will benefit from the outcomes, and those whose work might be impacted by the change.References: PRINCE2 Foundation Manual

An objective of the 'Directing a Project' process in PRINCE2is to give authority to deliver the project product. This process is where the project board makes key decisions and exercises overall control while delegating day-to-day management of the project stages to the project manager.References: PRINCE2 Foundation Manual

In PRINCE2, the Senior User role represents the interests of those who will use the project's products, those for whom the products will enable benefits after the project is complete, and any others who might be affected by the project outputs. This role is essential in ensuring that the project delivers products that meet the users' needs and achieve the desired benefits for the organization. References: PRINCE2 7 Foundation Handbook and official training materials.

The Controlling a Stage process is used by the Project Manager to maintain focus on the delivery of the stage's products within the agreed tolerances. This involves assigning work, monitoring such work, managing issues and risks, and ensuring that the stage remains on track in terms of time, cost, quality, scope, risk, and benefit performance. References: PRINCE2 Foundation official documentation and study materials.

During the 'Maintain' step of the 'business case management' technique in PRINCE2, the project manager assesses the ongoing viability of the project against the business case, including whether the outcomes are likely to deliver the expected performance improvements post-project. This is a continuous process that ensures the project remains aligned with business needs and expected benefits throughout its lifecycle.
References: PRINCE27 Foundation documentation on business case management.