I use the compound for angle cuts and threading. However, for non DRO machines (or other means to measure z axis movement), the compound proves useful for precision z axis movement. Align the compound parallel to the spindle axis. You can now lock the carriage and move precisely in the z direction.
Another use is for cutting to a shoulder. I would set my carriage stop so the cutting tool just touches the face of the part and zero the compound. I then back the carriage off and dial in the compound for the depth of the cut. I can then cut to my shoulder using the carriage knowing that I will not overcut my shoulder. Kind of like setting a stop on a drill press.
One more use is for making sub-thousandths turning moves on the lathe. The compound it set at an angle of 5.74º to the z axis so a movement of .001" of the compound causes a movement of .0001" of the tool in the direction perpendicular to the spindle axis. It isn't perfect as there is a significant movement in the z axis direction as well but if you are turning a press fit, for example, it increases your control of the diameter dimension. This can be carried further by setting the compound angle to .57º and get a 100fold increase in resolution.