Quant,
Obviously many people would equate GMAT score with IQ. We could disagree with that perception, but it exists. Another reason that I would like to add to the ones mentioned above is to judge your choice of MBA school. Knowing your school, I might ask the GMAT score to see if you went there because you could not get into a better school in your town. So if you get interviews and they ask you about why XYZ school, you need a good story regarding the quality of education blah blah blah. As opposed to “it was convenient and their GMAT requirements are low.” You want to sell your school as a great decision. I get the “Why XYZ school?” question in most of my interviews.