Might want to give the old help file a try:
State of the running Virtual Machine with all its applications inside can be saved to disk for continuing executing guest OS at a later time. This is called suspending of the Virtual Machine. When suspending, Virtual Machine state is saved to hard disk in a .sav file. After this no matter how long you will not touch it, will you shut down your host computer or not, you may return to the saved Virtual Machine at any time and continue running the guest OS from the point where you stopped.
You may configure Parallels Workstation so that all the Virtual Machines will be suspended when you press the Power Off button, or so that you will be asked whether you want to suspend or to power off the Virtual Machine on this action.