The direct answer
ROAS measures revenue generated per rupee of ad spend, which is useful for in-platform optimization but says nothing about profitability. CAC — what it actually costs to acquire one customer — measured against customer lifetime value is the metric that tells you whether the business is healthy, so most businesses should anchor decisions on CAC:LTV rather than ROAS alone.
Where ROAS is still useful
ROAS is a fast, platform-native signal for day-to-day optimization inside an ad account, especially for comparing creative variants against each other in the short term. It's a tactical metric, not a strategic one.
Why CAC:LTV is the strategic view
A campaign can post a strong ROAS while still being unprofitable once fulfillment, discounting, and churn are accounted for. CAC against LTV forces that full picture into the decision, which is why it should be the metric a business reports on at the leadership level.