1. For those of us who have been on the racetrack before, whether in competition or a performance riding school, decisions on cornering lines while street riding usually come as second nature. Little concentration is spent on it, since the “classic” racing line has been ingrained into our visual cortex, either by racetrack instructors or racing experience. And while it's surprising to witness countless riders weaving indecisively while bending into a turn on the street, it's just as surprising to watch riders using a racing line in cornering situations where conditions warrant otherwise.
The classic racing line generally involves a wide (outside) entry, with a graceful swoop to the apex allowing you to get on the gas early and accelerate to the exit with as little lean angle as possible. This occasionally means staying on the outside of the lane as long as possible before turning in, so as to minimize the amount of time your bike is leaned over. It takes a bit of cojones from less-experienced riders to use this type of line because they feel safer turning in early, away from the paranoia of dirt on the outside of the turn or running off the road itself.
2. The benefits of the racing line are numerous. For instance, it allows you to see more of an entire corner and the road beyond it before you commit to the entry. The less time your bike is leaned over, the better you'll be able to deal with road debris and other various hazards. And it usually permits the smoothest arc through the corner without abrupt throttle changes, which could upset the chassis midcorner. When we talk of the benefits, we don't mean only at elevated paces; you will reap the rewards at any speed.
Of course, any line may and/or should be modified because of a bump or any other obstacle. You need to be able to survey the situation ahead and plan your lines to give you the most advantage. There are situations where a racing line isn't going to be the best choice.
3. Straying too far to the outside in blind right-handers can be hazardous, because oncoming Joe and Ethel von Motorhome all too often cross the centerline into your lane, looking to add that nice little hood ornament they're missing. The same can be said of blind left-handers; Joe and Ethel are just as likely to overcook a corner, and if you should clip the apex going the other way with your body and bike actually leaning over the centerline, well…
Classic racing lines are a bad idea on freeway on/offramps because fuel and other slippery spillages are flung outward by centrifugal force. A tight inside line is the prudent choice here.
4. You've got to think about lines in the urban jungle as well. If you're about to make a right turn around a corner with parking lot exits, it's a good idea to stay wide and signal at the last possible moment—that way cars exiting the parking lot won't think you're turning into the lot and bolt out in front of you. While riding on multi-lane freeway curves, choose lines around the surrounding traffic that minimize their blind spots, as well as offer the best escape routes.
A lot of riders don't pay attention to picking lines, either because of their lack of experience or their belief that lines matter only when you are interested in speed. Deliberately establishing good habits for approaching and negotiating corners can go a long way toward not only increasing your fun factor, but survival as well.