With the advance of CNCs , spotting drills became a neccesity , The solid bodies allow long lengths to be held out of toolholders . Your cycle time is reduced because they do not have the small pilot drill , thus reducing your drilling depth on z axis . They are much easier to program for CNCs also . You know the angle and the desired width you need , so depth is a simple trig calculation . As far a the different angles ? Many DOD jobs require different angles for different applications . They tie them up and they check them closely . I use spotting drills over center drills for one reason . I can run them at a higher speed and feed . Center drills may go from 1/8pilot to 1/2" body which changes your surface speed dramatically causing them to break , dull , load up etc . They are also very easy to resharpen .