To me one of the most fascinating thing that can be done on a mill is circle interpolate, that is use a small cutter to make a large hole or arc.  The fact that it is basically impossible to do this operation without a rotary table or CNC control led me to choose both.  CNC permits the operation to be done along with any other milling operations with minimal setup changes.  The rotary table mounted perpendicular to the spindle, or “vertical” provides a unique way to machine multiple angles without re clamping the work piece.  I take great joy in something as simple as milling four flat sides onto a round piece of stock.