In more recent versions of Parallels they've added a "Pause" action in addition to "suspend". If you like to run a whole bunch of VMs at once, pause will near instantaneously put on hold the execution of the VM thus reducing the CPU usage for a single VM from around 40% to around 5%. This is better than leaving the VM runnning in the background when you're not using it. Confusingly the older version's 'Suspend' action had the pause icon, whereas the current dev build doesn't have an icon for suspend at all?!