8. Mix parameter for distortion pedals: in order to mimic some pedals which have that feature.
If we mimic such pedals, we would have a mix control. I have got close to zero responce for the mix parameter in the amp section (I must admit it is not documented in the manual). Parallel mix with distorted signals is not that sexy.
Try mixing a TS808 and the clean signal in front of an amp. Sounds awesome for low to mid gain sounds bringing clean lows to the mid-boosted tone of the Tube Screamer. There is a TS808 based pedal called Sparkle Drive that does something like this.