To avoid the hassle of ever not having one when a lifty decides to actually enforce the rule...and it's happened many times. From experience, I know how much it sucks to have either hike back to the car to get it, or wait in line forever and shell out $10 at the rental shop. I keep one in my pocket as often as I can remember.
14 NeverSummer Proto HD . 13 Never Summer Cobra . 12 Gnu Rider's Choice C2PTX
13 Now IPO . 12 K2 Formula . 11 K2 Formula
13 NB x 686 580