For the occasion, yesterday VMware published a new 29-pages paper about it: Host Profiles: Technical Overview.
The document covers several use cases, including the ones that involve advanced profile editing and customization, like when an administrator needs exceptions in host configuration variability.
Interestingly, the paper introduces the new marketing pitch for vSphere (emphasis added):
VMware vSphere 4.1 (“vSphere”) is the industry’s first cloud operating system, transforming datacenters into dramatically simplified environments to enable the next generation of flexible, reliable IT services…
In 2008 the company used to refer to vSphere as a Virtual Datacenter Operating System (VDC-OS). The company still thinks in this way. What slightly changed is the definition: from VDC-OS to C-OS.