Vinay Pai has a post today that I think spells out one of the key benefits of Service Level Automation. Remember, the key aspect of SLA is knowing what capacity is required to maintain target operational goals. A basic SLA environment will assure that only the necessary capacity is active at any time.
So, if capacity is not being used at any given point in time, why have it consume power or cooling at all? Some "automation" products require underused physical infrastructure to remain running in order to support their management layers--just in case. This is unfortunate, as an idle hypervisor is just idle capacity. Its not serving a current business need.
A truly efficient SLA platform is aware of the power controller states of each of its physical servers, and can power down unused servers. Servers are only turned on when they are needed to meet some aspect of the system's service level goals.
Note Vinay's description of the QA labs at Cassatt. As you might expect, he pushes the limits of what a SLA datacenter must endure, yet can always scale his power and cooling needs to his current workload. Can you say that about your datacenter?