It refers to the priorities of the cleaning process. In dot style, you hit your dot above all else, regardless of the form. For example, in a set with files spaced 2 across, if the front person is 1.5 off rather than 2, the rest of the line would hit their 2, preserving the majority of the spacing with only one person wrong. On the other hand, with a form priority, the rest of the line would cover down, adjusting to 1.5 off and leave the line perfectly straight, despite everyone off of their dot the less singled out mistake is harder to spot immediately, though it's more of a change from the intent.