See also http://www.pizzamaking.com/forum/index.php/topic,8405.msg72655.html#msg72655
. As noted in one of the posts in that thread, Papa John's routinely uses a dough docker for all of its skins. I believe that in PJ's case it helps open up the dough balls easier, possibly by partially dismantling the gluten structure, thereby reducing the natural propensity of the dough to shrink back, especially if the dough is cold when worked. This is a fairly old video but you can see a PJ worker using a dough ball, quite aggressively in his case:
. According to Tom Lehmann, one is supposed to only make a single pass across the skin. Otherwise, according to Tom, you are likely to end up with what he calls a "poker chip" (see his post at the PMQ Think Tank at http://thinktank.pmq.com/viewtopic.php?f=6&t=194&p=776&hilit=#p776
). I have seen PJ workers work a skin with a dough docker unmercifully, such that the rim, even after baking, was riddled with holes.
Based on my experience, I would say that a dough docker is most commonly--and properly--used to make cracker-style skins, typically in conjunction with a roller or sheeter, as Don noted. For other styles, it is usually a crutch and as a way of using cold or underfermented or insufficiently tempered dough.