The main purpose of a cross fader is to easily morph (cross fade) between two or more signals without having to change the levels of all signals simultaneously. It is essentially a mixer but with one control (knob/CV) which makes it ideal for performance, automation or smooth morphing.
The S116 has three inputs A, B and C. And has two outputs. The main output cross fades between A, B and C. While the other output cross fades between A and C. Both manual and voltage control is provided. Note that the indicated diagram on the panel refers to the main (A, B, C) output. The other A, C output should be obvious.
The S116 can obviously be used to cross fade both Audio and CV without.