Snapshots are a wonderful feature found in just about all of today’s hypervisor products, including Xen, Hyper-V and vSphere. However, they’re a physical impediment when it comes to leveraging some hypervisor features. Let’s take Hyper-V, for example. While you may find a reason that calls for the use of a passthrough disk, make sure you understand that you will lose the ability to snapshot that particular disk. You can still take snapshots of any virtual disks that you may have configured in your virtual machine.
Another point: Believe it or not, you can still perform a Live Migration of a virtual machine that is configured with a passthrough disk, but you will not be able to perform the Live Migration in a way that results in no downtime. The passthrough disk has to be unmounted from one host and mounted on another, meaning that it’s not possible to avoid at least a little bit of downtime.