A: You probably only need vCloud Director if your business is an enterprise or service provider. This solution aggregates the resources of one or more vCenter Server resource pools for the purpose of provisioning those resources to one or more tenants. It elevates the boundary of administration above the level of the individual vCenter Server.
vCloud Director’s most important value proposition is its support for multi-tenancy. It can logically separate customers (and their resources) from each other in a range of ways. Customers are delivered the resources they need based on a range of configurable allocation models.
As a metaphor, if vCenter Server is the solution that collects ESX/ESXi servers together, vCloud Director is the solution that collects vCenter Servers together.