When you push your networking, storage, and other infrastructure from on-premise to the cloud, you can let go of your on-premise real estate and shift the burden back onto the cloud vendor. Google absorbs the cost of power, cooling, management, etc.
You no longer need to spend on CapEx. Instead, you are spending on consumption, so your CapEx moves into OPEX and then on the utility. That's the generic use case for why somebody would move their workload to the cloud.