What's an example of a metric used to measure value?

The selection is correct because cart size is a direct indicator of the monetary or strategic importance of a transaction, shifting the focus from the sheer quantity of conversions to the actual value those conversions generate for a business. While metrics like time spent on site or page depth measure engagement, and cost-per-click measures efficiency, cart size provides a tangible data point that allows Google’s AI-powered Value-Based Bidding strategies—such as Target ROAS (Return on Ad Spend)—to distinguish between a high-value customer and a low-value one. By optimizing for cart size, the machine learning algorithm can prioritize bidding on users who are likely to spend more per transaction, ensuring that marketing budgets are allocated toward the most profitable outcomes rather than just the highest volume of clicks or basic site interactions.