An important aspect of VDI is to understand which clients are going to use the VMs you publish through RDS. Different clients require different VMs. Because of that, there are two options in publishing VMs: Pooled and Personal.
Pooled VMs are VMs for users that need to access a certain application but will not need to use the OS itself and/or save files on the VM. A Pooled VM is usually used on kiosk machines, or where the user needs to use an application that runs on a Windows Client OS, so session-based is not an option. A Pooled VM works in a non-persistent fashion. That means that the VM will return to the original state after the user logs off the VM. The Pooled VM lifetime works like this:
Note that, after the user logs off, the VM is recycled and is available for another user to use. It is important to calculate how many VMs will be available given the number of users. For example, if you will have ten users, you don't need ten VMs available, but you need to...