Optimizing your budget involves shifting spend away from underperforming campaigns or products toward those with proven results, increasing the likelihood of greater sales and ROI.

• When you want to increase for low-performance/decrease for high-performance products or campaigns to improve overall performance
• When you want to try different budget allocations to ensure your ad budget can cover a full day
• When you want to increase for high-performance/decrease for low-performance products or campaigns to optimize your budget or increase purchases

The correct answer is: When you want to increase for high-performance/decrease for low-performance products or campaigns to optimize your budget or increase purchases

Explanation: You should reallocate your ad budget when you want to increase spend for high-performance products or campaigns and decrease spend for low-performance ones. This helps optimize your overall budget, direct resources to what works best, and increase purchases—ensuring your investment drives the greatest return.

Reference:  https://advertising.amazon.com/library/guides/budget-rules