Today, if you need more server or storage capacity you need to purchase new equipment. When you move to cloud computing you simply request and pay for only as much more as you need. And if the need was short-term you can turn it back down when you're done and stop paying for it.
When your data and systems are located in the cloud your company can keep working even if your premises become unavailable. Your people can always work from anywhere they can access the internet, on whatever device they prefer to use, whenever they want. That's true agility.