I originally learned to touge using both lanes, but I've come to realize after talking to Nar (scarsofcarma) and also Johnny Tsunami, that single-laning has more merits. Not just in the sense that it forces you to learn better speed-control, but also because it is safer. In my experience it's important to leave that other lane open as an escape zone. Obstacles like boulders, tree-branches, deer (living or dead) can find themselves in your path, so by single-laning you are leaving that other lane open in case you need it for an emergency maneuver.