The device licensing uses the license even if the device is in service or out of service. Within 4.2, you can set the devices to device only which does not take a license but you have to login using hot desking account to use the phone and it's features (Excludes calls to the operator and emergency services)
With the Traditional licenses a license is consumed on programming the ACD device the login are restricted to these devices. Hot Desk ACD agents can login to Hot Desk enabled phone and an ACD license is consumed upon login.