This is the first of the theatrical rigs to use two spot lights instead of one. Each lamp is placed in line with the actor one slightly to the left and the other slightly to the right.
With two lights there is now light to both sides of the face. There are fewer areas of heavy shadow on the actor. There are now shadows cast in two directions. This is most obvious on the stage although they may show on the face or on the actor’s body too. With shadows in two directions we move away from any attempt to create natural looking lighting and we focus on lighting for emphasis and to illuminate the performer.
Using two lights has very little impact on render times compared to using a single light.