The lane-divider line on a road-whether a double yellow, broken single yellow or white line-is usually (and actually, should be) the demarcation zone for street riders. It marks the limit of usable pavement for that particular direction of traffic, and is basically there to facilitate the flow of traffic and prevent head-on collisions. Staying on your side of the yellow/white line through corners usually means you're safe from oncoming traffic. But we see far too many riders dangerously stepping over that boundary, even though they're technically on their side of the road.
Since a motorcycle uses lean angle to turn, its tire tracks are not in line with the rest of the vehicle, unlike a car. This means that though the tires may be at one point, the rest of the bike-and probably even more critical, the rider-will actually be far inside that point. While this poses no problem with right-hand turns, turns to the left create a hazard that many riders unwittingly step into, especially in blind curves. They may be "hitting their apex" just right, but what they don't realize is that much of their bike-and most of their body-is actually over the lane divider, putting themselves at great risk for a head-on collision.
Many two-lane roads are narrow enough that a car or truck can fill up nearly a whole lane. Should they encounter an oncoming hazard, there's not much room to maneuver in order to evade that danger. And that's not even taking into account those drivers who slightly wander over the line into the wrong lane due to distractions or just plain poor driving skills. Or what about a rider approaching in the opposite lane staying wide before turning in so that he won't have to use much lean angle?
Think about it: All it takes is one vehicle traveling at 30 mph, and the other moving at the same speed, to equal a closing speed of 60 mph. Around a tight, blind left-hander, that doesn't mean much time or room to recognize the oncoming hazard and take evasive action. Why expose yourself (and perhaps another rider) to this risk? Be cognizant of your body's location when you carve that next left-hand turn, and keep your wheel tracks far enough in your lane to prevent having to lean your body (and bike) over the lane-dividing line. Learn to regulate your speed in those corners also, so that you won't be tempted to use that pavement in order to make the corner.