I think knowing the archetypes and the theory of the hero's path help us identify and recognize things in different manner we usually do. In this way we can come up with different perspectives over a single character and we can come up with different reasons why is he doing or thinking, and even come up with some theory of what is going to happen.

Also having all this classification at our disposal we could be inspired to write some story about a hero, following the hero’s path theory and accomplishing it almost without any effort on getting ideas to make a plot.

Finally all this knowledge will help us at the time we read, or at the time we write. We can use this as our guidelines or as something we don't want to cross, or get close to. So this information isn't at all useless, if it was ever think at it that way, but some useful information for our lives and our future as reader or writer.