When and why factory used dual snorkel?

Unsilenced or open aircleaners let in air over the entire surface of the filter. Sealed aircleaners (the ones with snorkels) only have the snorkel opening to let in air -- it can be a serious choke point. You can only make a single snorkel so big (limited by the depth of the filter element), so the only way to add more area is to add a second snorkel. I don't think it's a joke or a gimmick at all -- I think if you duct taped one of them closed, you would notice the difference at WOT. Look at it this way -- look at the diameter of the circle on the top of the carburetor -- that would define the area of air intake that would be ideal. Anything smaller than that is choking your carb at WOT. Most snorkels are way smaller diameter than that.