Sanding belts get the smallest signs of wear when being used, which show in the sanding result. When using a sanding belt set parallel to the feed direction they show from the beginning to the end of the workpiece, if the oscillation is turned on, in form of wavy lines.
With a sanding belt set slightly diagonal to the feed direction, the errors form diagonal tracks, which appear as an area because of their juxtaposition. Because of the diagonal set, more abrasive particles have the opportunity to show on the workpiece then with a straight set of the sanding aggregate. Thus, there is a more thorough mixing of the tracks, which visually gives a "flat" appearance.
Due to the slightly angled cut, the fibers are sheared off crosswise what leads to a clean cut and saving of energy.
These effects cannot be achieved with diagonally loaded workpieces.