Choosing between Campaign Budget Optimization and Ad Set Budget Optimization is rarely a permanent decision. Many experienced media buyers use both, but at different points in a campaign. Campaign Budget Optimization, or CBO, places one budget at the campaign level. Meta then distributes that money among the ad sets according to their performance. Ad Set Budget Optimization, or ABO, gives each ad set its own fixed budget. ABO is usually the better choice for testing because it guarantees that every audience or creative receives enough spend to produce useful data. Without that control, Meta may direct most of the budget to an early leader before the other ad sets have had a fair chance. CBO becomes more useful when the campaign has several ad sets with a reliable history of conversions. At that stage, Meta has enough information to move the budget toward stronger performers. The media buying team at Superscale explains why this automated allocation can outperform frequent manual changes once the campaign is ready to scale. Using CBO too early can produce a misleading result. An ad set that performs well in its first few hours may receive most of the budget, even if that early performance was simply good luck. Current guidance, including the process Cropink lays out here, generally recommends testing with ABO and moving proven winners into CBO. Accounts with smaller budgets may need to use ABO for longer because CBO needs enough daily conversion data to make sound allocation decisions. bm2500 also provides an example of how this choice works with real campaign budgets.