Cost optimization has two parallel paths. One is "buying cheaper" (commitments·Spot, covered yesterday with SP·RI), the other is "using only what you need" (rightsizing). The latter is more fundamental — no matter how good a commitment discount you buy, if an m5.4xlarge is consistently using only 5% CPU, that''s the same as buying an m5.large at 8x the price. Moreover, commitment discounts and rightsizing compound multiplicatively: applying a 72% commitment discount to an 8x over-provisioned instance is still vastly inferior to first reducing that 8x to 1x