By using a snapshot, you preserve the state of a VM so that you can return to that state any time you want without creating multiple VMs. Use a snapshot as a restoration point during a linear or iterative process (for example, installing update packages) or during a branching process (for example, installing different versions of a program). You can also use a snapshot as a baseline for a VM.
http://www.embotics.com/documentation/index.html?vm_snapshot_portal.htm