Doesn't have to be a system process. I just don't want to have to log in at the console to start a VM. And I don't want the VM to stop/freeze just because I close the window.
Hiding the Parallels window or moving it to another space is not nearly as safe as disconnecting from the VM would be.
Parallels server will probably offer the feature, but I think it would be very useful for the workstation/desktop version as well.