According to PRINCE2principles, the business case theme requires documenting the management actions necessary to ensure benefits are realized. This involves planning, measuring, and managing the realization of benefits, and it's critical for maintaining the relevance and justification of the project. References: PRINCE2 Foundation Handbook, Business Case Theme section.

A leadership activity within a PRINCE2 project involves several responsibilities, one of which is agreeing on work packages with team managers. This agreement includes specifying the tools and techniques to be used for product delivery. This activity is crucial for ensuring clarity and mutual understanding of how work is to be conducted, facilitating effective delegation and accountability within the project team.
(PRINCE2 7 Foundation Study Guide, AXELOS)

During the 'Initiating a Project' process, the project manager develops key information, including the detailed Project Initiation Documentation (PID), which enables the project board to decide whether to proceed with the project. This information outlines the approach, plans, and controls that will govern the project, providing a foundation for detailed planning and informed decision-making by the project board.
PRINCE2 7 Foundation materials on the 'Initiating a Project' process.

As part of the 'controlling a stage' process, the actions taken include authorizing work to be done (2) and taking corrective action (3) as necessary to manage the stage effectively and keep the project on track.
References: PRINCE2 Foundation Training Manual; PRINCE2 2017 Foundation handbook.

The purpose of the Change theme in PRINCE2 is to identify, assess, and control any potential and approved changes to baselined products. This theme provides the mechanisms to manage and control changes, which may affect the project's agreed-upon scope, products, timescales, or costs. It ensures that all changes are assessed for their impact and only implemented with appropriate approvals.
PRINCE2 7 Foundation resources and materials.