On the SAA exam, cost optimization (Domain 4) accounts for 20% of the total. By weight alone it's smaller than security (30%), but this domain is tricky for a separate reason. Where other domains ask "what works," the cost domain asks "of the several ways that work, which is cheapest." That is, you must filter out the option that is not functionally wrong but simply costs more. So keyword mapping alone isn't enough; you must understand on which cost axis (compute, storage, network, operations), and at what trade-off, each savings lever cuts money.