If you do not publish device updates, then the user will experience no change. For example, a device that is running Office Communicator 2007 Phone Edition will continue to behave as if the user were homed on an Office Communications Server 2007 pool.
After you publish device updates, affected devices will be automatically updated only during periods of inactivity. After the last update is applied, the user will have access to the new features of Office Communications Server 2007 R2 that affect the device.