There are several different reasons. The first is that not all of our users are familiar with or comfortable using the object.method syntax. A large subset of our user base prefers function(inputs) syntax, and in that syntax there are situations where you don't want the left-most object to control which class's overload of a method to be called.
One concrete example is this: plot(ax, obj) where ax is an axes object and obj is an object whose class has a plot method. Which plot method should this call? The axes object is the left-most object, but we don't want it to have to know about every object that could be plotted in it. So many graphics classes will define axes as an InferiorClass, to ensure that plot call would call their plot method rather than the plot method of axes.
Another is that sometimes the order of the input arguments matters. If A and B are two classes that each overload the minus method, how can we use B's minus to compute A-B? B.minus(A) computes B-A which is not what I want. But if A and B have the same priority, both A.minus(B) and A-B would call A's minus. In this case B would declare A as an InferiorClass to force A-B to call B's minus.
