Importance of a Pencil?

I got a B in AP Calc last quarter thanks to all the "-2's" at the top of all my papers, because I used pen. (After the quarter ended I sat down with the teacher and added 2 to all my grades). I only use Pencil in Music Theory, never in math. I work faster, cleaner, and more accurate in Pen.

Btw: Only pen I use is http://p.pens1000.com/vp1/31002PIL.jpg

the one on the far left there