Just passed the 4K mark on my CX-5 GT. Over half way to my first service which I'm probably going to do myself. I've asked my dealer to send me the free oil change maintenance program which lists everything they do. Still waiting to receive but I think I remember it saying they change the cabin air filter. Is this necessary? What does it really do? I understand it's not hard to change but this is my first car that ever had one. What's the thoughts out there? Thanks