Listen man, there are many ways one can play a Guitar, and or hold it. The decision is up to you. Although, there are many confortable ways of holding a Guitar that can harm your hand, joints, arm, back, etc. Your teacher is trying to teach you the proper way of holding the Guitar for a longer lasting play without injuries and or stress on your fingers, palm, etc. I am an experienced Guitar player and I hold the Guitar exactly the way your teacher wants you to learn. It is optional of course.
Many famous Guitar players out there have awkward Guitar holding manners, because they were self taught, and they played the Guitar to their maximum confortability. The thing is that you will get confortable with any position, and or style as long as you spend the time on it, etc. I for one, experienced unconfortability when first teaching myself to do this same thing. Now, because of the practice, I can shred faster, and stretch my fingers wider to reach higher octave notes faster, rather than stressing my fingers to do so. Let me know if you have more Guitar related questions, because I have plenty of answers.
-Ron