The first rest is to let the dough develop gluten without you having to work your arm. We don't recommend using a stand mixer because the dough is a bit stiff, which will give your mixer a hard time. If you prefer, you could keep kneading the dough until it is smooth to skip the first resting period. The second rest is to allow the gluten to relax, so that the dough is easier for your to roll out. If your dough is ever too stiff for you to shape or roll out, just let it rest for 5 to 30 minutes, covered.