According to the ‘manage by exception’ principle, which aspect of performance sets limits against the...

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.References: (PRINCE2® 7 Foundation Handbook, AXELOS)