If I had to establish a large garden to feed a lot of people in a hurry, and I did not have the materials available to sheet mulch the area with cardboard, then I would probably till an area to start the initial process. Tilling, if done repeatedly will require a lot more inputs in order to keep up the fertility (food for the soil community that feeds your plants), and even the initial losses should probably be amended (as Wayne mentioned with tilling in manure). Tilling will expose your weed seeds, and break up weeds; some of these that are present will be multiplied by the process. So, although it seems like a labor-saving tool, tillage can cost a lot in labor expenditures due to weeding. I'm not sure what the savings in materials are that you can see in the tillage process.
If I had to grow a lot of food for myself and other people, I think I would have to till. Tilling worries me, mostly because I'm very afraid of eroding my soil. But I can see how tilling can save an enormous amount of materials and labor in its own way.
I'm not going to argue with Joseph's family history, or his methods, which certainly are great and to be commended; particularly in the high desert. I certainly could stand to learn immeasurably from his knowledge base. I chose this quote from his post to point out a few things. There is a big difference between running a roto-tiller and the harvesting of some carrots, potatoes, or garlic. I harvest with a spade-fork. While it certainly does disturb the soil, there are large masses of intact soil ecosystem left from which the carrots or potatoes or garlic separate, and these are likely (in my thinking) able to help re-inoculate the rest of the soil system with a balance of soil community members and provide some long-term stability to that system. Tillage, unless it is done with a single pass of a plow, does not allow such communities to be intact. Generally, these days, tillage is done with a machine which tends to not leave large masses intact in the soil. Even if tillage is done in a way that minimizes the powdering of soil, the masses are usually broken down into quite small bits in comparison to the harvesting of carrots with a spade fork. I am not a staunch advocate of zero disturbance, simply minimizing it. There is also a difference between no-till and no disturbance. No disturbance is impossible.
Long winded way of saying that I think no-till advocates may get better results if they don't try growing annual species or root crops. How could a proponent of not disturbing the soil grow something like carrots, or potatoes?
Hmm, is tilling sustainable? Hard to say. We've made it 10,000 years so far.
Interestingly, after visiting Le Ferme du Bec Hellouin, Eliot Coleman decided that he should start planting trees in amongst his annual market gardens.
Therefore, they tend to thrive in tilled soil, and do poorly in forest type soils.