There are many possible uses for the fader with Audio Input and Output. One of a feasible field is sound instrument. We made Sine Wave Oscilator with this instructable. It can make full use of its precious samping resolution.
Here is the setup. You will need split you audio output with stereo to dual mono cable. On one channel you connect the fader, and on another, you connect a speaker. Then you add a sine wave oscillator and a scale changer to fit the value frome fader to the frequency of the sine wave oscillator in your software. Now, you can finely control the sine wave oscilator in 16-bit resolution.
Here is a MaxMSP patch.