This procedure applies when you’re using a vertical mixer, such as a 6- or 8-quart tabletop model or a 12- or 20-quart stand mixer. For dough developed by hand on the bench, this instruction does not apply.
Vertical mixers like these need the baker’s assistance to evenly distribute ingredients and to develop a uniform gluten network in a dough. Developed entirely by machine, the bottom and the top portions of the dough become more elastic because they are agitated more vigorously by the dough hook. The middle portion of the dough receives less manipulation and is less elastic by comparison.