Metaphors Part 2

How or why might a metaphor be valued over a simile? What makes them so different? I understand that a simile is a comparison using "like" or "as", approximating something to something else, and that a metaphor is more of an equation to something else, but what, other than that, would set them apart? Why would we study an entire chapter on metaphors, but not on similes? They are both types of literary comparisons. What can a metaphor do that a simile cannot? I believe that metaphors can help the reader to see something old as new, and to see things in a new light. But I don't see why similes couldn't do the exact same thing. They, too, may be able to bring old information into a new light, and change your perspective on things. They too are extraordinary tools used to look at the world through a different lens than the one you’ve been using. So why are metaphors viewed as more important than similes? It seems to me that, due to their very similar nature, they would be equally important in literature.