PRINCE2 mandates the use of management stages in project management. These stages are critical control points used by the Project Board to review progress, assess risks, and make decisions about the project's future. This structure allows for regular monitoring and controlling of the project by breaking it down into manageable sections. References: PRINCE2 Foundation official documentation and study materials.

The principle of 'manage by exception' in PRINCE2 involves setting limits on delegated authority concerning time, cost, quality, scope, risk, and benefits. Here, the aspect of performance that sets limits against the cost of aggregated threats is "Cost". This includes setting tolerances for what can be considered acceptable deviations from the plan before an issue needs to be escalated to a higher authority. Managing by exception helps in efficient use of management time and focuses on deviations that might affect the project's success.
(PRINCE2 7 Foundation Handbook, AXELOS)

Explanation
Reference https://www.prince2primer.com/tailoring-prince2-methodology/