Rotary table uses:
To machine spanner flats on a bolt
To drill equidistant holes on a circular flange.
To cut a round piece with a protruding tang
To create large-diameter holes, via milling in a circular tool path, on small milling machines that don't have the power to drive large twist drills (>0.500"/>13 mm)
To mill helices
To cut complex curves (with proper setup)
To cut straight lines at any angle.