Which metric is used to measure efficiency in sponsored ads campaigns?

Return on Ad Spend (ROAS) is the primary metric for measuring efficiency because it directly quantifies the revenue generated for every dollar spent on advertising. A higher ROAS indicates a more efficient campaign. Impressions measure visibility, not financial return. Click-through rate (CTR) measures engagement but doesn't directly reflect profitability or efficiency. Sales measure total revenue but don't account for the cost incurred to generate that revenue, making them an incomplete measure of efficiency.