When on, any subsequent calls cannot be intruded on until the user's private call status is switched off. The exception is Whisper Page which can be used to talk to a user on a private call.
Note that use of private calls is separate from the user's intrusion settings. If the user's Cannot be Intruded (User | Telephony | Supervisor Settings) setting is enabled, switching private calls off does not affect that status. To allow private calls to be used to fully control the user status, Cannot be Intruded (User | Telephony | Supervisor Settings) should be disabled for the user.
If enabled during a call, any current recording, intrusion or monitoring is ended.