Public cloud offers the biggest opportunity for cost savings. IT becomes a utility supplied by your cloud provider; your business no longer incurs hardware or maintenance costs and you pay only for what you use. Economies of scale enable the cloud provider to provide these compute resources often at a much lower price than the cost of hosting them in-house.
Public cloud offers the greatest potential for elasticity. To achieve this, your cloud provider needs to give you the tools to rapidly (or automatically) provision and decommission compute resources so they ramp up and down in line with fluctuating business demands. Because you’re paying only for what you use, this maximises cost savings. You also shift risk to your cloud provider, which is locked into agreed SLAs.