A. There are two architectures for VDI--static and dynamic. With the static architecture, each user always connects to the same virtual machine (VM) that exists and is maintained between sessions. This means for every user, you need a VM, which obviously requires a large amount of storage for all the VMs.
With a dynamic architecture, the VMs are not persistent and when a user connects, a new VM is created based on a master template, the user personality is placed onto the new VM and applications are made available through application virtualization, giving very fast availability of the session. Once the user disconnects, the VM is destroyed. In reality, the VM is not created when the user connects; the VDI solution maintains a pool of "ready" VMs to expedite the user connection experience.
While dynamic architecture is more complex because of the provisioning requirements of the VM, profile and folder redirection, it is the best practice because it actually reduces management overhead since you're not patching the OS anymore; you just update the master image. In addition, you'll have fewer VMs, because you only need to host VMs for the number of concurrently accessing users.