It is a "perk". The military sends overseas away from many of the comforts of home. So they do little things to help with morale, such as provide IVG lines for cheaper phone calls to the States, an APO which allows you to send and receive mail overseas at domestic rates, and limited use of NIPRNET during off hours. And much of the time the NIPRNET that is being used is at the on base library.
It is a worthwhile benefit.