Below are a pair of graphs showing lambda versus voltage for narrow and wide band oxygen sensors. It is easy to see that the wide band has a much more linear curve over a much wider voltage range, hence the name "wide band". This makes for much greater tuning accuracy and the ability to tune for very different air/fuel ratio (AFR). On the left below is a narrow band sensor graph and on the right is a wide band. You can easily see why wide band is far superior for tuning AFR over the entire range.
GenBoard/Manual/WBSensor for wide band sensor setup
GenBoard/Manual/NBSensor for narrow band sensor setup