You need to know where to land.
That might seem obvious, and the obvious solution, when dealing with modern military aircraft, is to place a waypoint, or steerpoint, on the airfield.
But even so, that doesn't set up an approach, it merely puts you above the runway.
TACAN provides a reference point that you can work from.
In this video I explain how to prepare and use a TACAN approach. In a previous video I explained how to tune to a particular TACAN channel. Here I explain how to use a bearing to the TACAN to set up an approach.