Dan explained that if you leave the edges at tip and tail of the skis as sharp and defined as the machine makes them, you will have a hard time either initiating a turn or trying to come out of a turn on the slopes. This is because the sharpness in the tip and tail works to continue your skis through the direction of travel either straight, as you shift to turn, or through the turn, as you shift to come out of one.
After detuning, the edges are deburred with either a fine diamond stone or a deburring pad. As it sounds, this process takes off any sharp little burrs not filed off by the edging machine.
Jack and Dan's Tip: Not detuning the tips and tails is the step most ignored in the at home do-it-yourself tuning process and can make for hard work on the slopes, so remember: SDD the ski; Sharpen, Detune and Deburr.