When multiplying in baking, should I follow directions all-at-once or batches?
When making pie crust, you want to a) keep your fat(s) cold and b) avoid over-working the dough, both of which are difficult to do when working in large batches. Cold fat, evenly distributed throughout the dough, will steam and melt away during baking; that leaves the air pockets in the crust that cause flakiness. Developing the gluten in your dough is necessary for a strong, elastic crust, but if you develop too much gluten, your crust will become brittle and tough. Working in small batches allows you to thoroughly combine the flour and fat until you've reached the "pea" stage, and then incorporate your water just enough to bring the dough together for gentle rolling. The best thing you can do to pie crust is to handle it as little as possible.

If you're using a large food processor or stand mixer to "knead" bread dough, you could get away with making more than one or two loaves at a time because you want to develop your gluten to a much greater degree than you do with pie crust. Be sure, however, that you mix/sift together your dry ingredients thoroughly before adding the liquid components of your dough whether you're kneading by hand or machine.