Pay attention to the new advertising report that Amazon recently released. This report allows you to see the performance of your campaigns on a daily, weekly, monthly, or quarterly basis. In other words, it helps you identify which campaigns are delivering exposure, clicks, and sales effectively.
How to get the most out of it:
Download the report: Reports - Sponsored Products - Budget.
Filter and display only the campaigns with a positive ACOS (Advertising Cost of Sales).
Sort the results from low to high based on the "Average Time in Budget."
Identify every campaign with an ACOS under 100% and adjust the budget accordingly.
In practice, any campaign with a good ACOS that is limited by budget is a campaign where you might be missing out on potential revenue. Therefore, there's no logical reason for such campaigns not to be consistently at 100%.
Make it a weekly task to explore this excellent report and optimize your campaigns accordingly.
Best of luck!