The Vapor faders refers to the stereo output of the crusher. If you open the I/O Level window you can gauge the input. Note that the internal structures allow internal overload close to +100dB! Only the output levels should be under 0dB because of the limited resolution of your soundcard.

The Effect faders refers to the stereo output of the effects.

The Dry faders refers to the Dry Sum to which each element of the crusher can be route using the send faders.

All volume faders have their own fading delay which allows smooth fading and muting - even with a massive volume change resulting from using the undo/redo function or altering another parameter! 

Open the DSP Structure window to see which element of the crusher will be affected if you move the faders or change the values.