The Smith Vantage helmet lets you control the air vents with two separate sliders... one for the front half of the helmet, and one for the back half of the helmet. I'm kind of curious, why would you open just one or the other? What is the scenario that you would close the front but open the back and vice versa? I'm thinking there must be a reason else they wouldn't have made this feature, but I'm not sure exactly why. Can someone shed some light on this?