Soooo glad I came across this thread. I had a pair of Mk3d's and no-one else knew what it was for either. I figured out a use for it though and the benefits were amazing. I mix music at a much higher BPM (say 140-150) when mixing at these speeds, 'touching the record' to beat match would usually always mean you were either fractionally too fast or slow. The easiest way to remedy this was to use the pitch control exclusively while 'in the mix'. However, the track would always take a little time to come back after it had drifted out due to the motor on the technics.
Using the RESET BUTTON
If you apply a little pressure to the reset button the light will temporarilly come on and then off when you release it (i.e. you don't need to depress it fully). I found the best way to hold it was if you grip the turntable so that your thumb is on top. That way you can bounce the button with your thyumb and watch the light go on and off. While the track is playing this provides momentary speed reduction or increase (depending on the position of the slider). By working out which track is faster or slower and therefore which button you need to depress momentarily you can trim the mix precisely and quickly (similar to the +- buttons on a CD player). Be careful though because the further away from the zero point you are, then more impact depressing it has. Additionally if you accidentally depress it too far, it will lock and throw the mix out completely (Dancefloor disaster). With a little practice your beatmatching with technics can become tighter using this extra technique.
Now I don't know if this was what they designed it for but it really worked for me. Have a go and see for yourself. I would be interested to know if anyone else can utilise it to the same effect.
