Deciding when to use ad set level budgeting in Facebook campaigns hinges on your testing phase and performance data maturity. Ad set budgeting shines when you have identified winning audience segments that deserve dedicated spend allocation, or when you're running parallel tests where different creatives need isolated performance measurement. Rather than allowing Meta's algorithm to shift budget dynamically, you maintain fixed spend per ad set, which simplifies attribution and prevents the platform from over-investing in marginally profitable variations. E-commerce brands running regional campaigns or vertical-specific audiences often see better ROAS when they bypass algorithm distribution and manually control where each dollar flows. This method requires more hands-on management but rewards careful strategists with predictable scaling paths and reduced wasted spend on underperforming segments.