I instruct using a PC based system (Jeppeson Flight Pro) to complement my IMC training. PC software is not much use to demonstrate how the aeroplane reacts to P.A.T but is essential to cut down training hours. For instance NDB tracking, NDB and VOR holds, DME arcs and all kinds of procedures...especially if you vary the wind. The real benefit over the aeroplane is being able to freeze the system at a point and then to replay with images actual track over the ground.
Since the 'sim' is not approved it does not cut down on training hours for the issue of the rating, but it does make the student a better pilot with much more experinece than if he had just trained in the air at his local radio aid/facility/procedure.