Setting the policy to Enabled turns on PluginVm for the device, as long as other settings also allow it. PluginVmAllowed and UserPluginVmAllowed must be True, and either PluginVmLicenseKey or PluginVmUserId must be set for PluginVm to run.
Setting the policy to Disabled or leaving it unset means PluginVm isn't on for the device.