This is a scaled axis value that will never exceed -1.0 and 1.0. It is intended to be used as a scale which you can apply to velocity vectors or for positioning objects onscreen. This normalized value is much more convenient to use than the rawValue property because you don't have to deal with the varying min/max axis ranges provided by different input devices, allowing your application to handle all axis data in a uniform manner.
The normalized value will range between 0.0 and 1.0 if the axis' min and max properties are greater than or equal to zero. This is commonly used by analog triggers on gamepads, touchscreens, touchpads, mice, and trackpads.