"One of the first lessons in economics is that of the beneficial effects of specialization. We're all better off if we specialize in doing something that we do better than others. Joe the Mechanic is better off if he focuses on mechanics, not sewing. And Suzy the Seamstress is better off if she sews than if she tries to fix cars for a living. And they're better off if they trade their services.
Now we can extend this to the greater economy. For a long time, travel and lack of technology were limiting factors in the amount of specialization we could have. Because of this, we had some built-in robustness. A large number of people needed to be involved in food production, and most important services had to be available on a local level.
Today, the ease of worldwide travel and productivity/communication gains from technology have allowed us to become more and more specialized. This is generally a good thing, as specialization makes everyone effectively richer through lower prices and better earnings. However, this high level of specialization has made us increasingly dependent on the 'grid' of modern life.
For example, only 2% of America's population is involved in agriculture. Technology has allowed farmers to become incredibly productive, decrease the amount of human labor needed and driven down the price of food. There isn't a demand for the huge amount of farm labor that their was in the past, so the population has moved on to other professions (mostly service-based).
However, America is FAR from food-self sufficient, and individual cities are even less so. We rely on massive imports from around the world and a network of trucks to move food across the country and into our cities. We've all specialized OUT of agriculture and rely on the grid to feed us. In normal times, it works fine--you don't have to spend hours and hours struggling to work a small farm, and can instead focus on working at your job.
It's the same story for energy, manufactured goods, water, you name it. Our clothes are made on the other side of the planet, electricity is delivered in from dozens or hundreds of miles away. Again, this is generally a good thing, as it gives us lower costs and often better quality (Samsung is better at making TVs than I am). And it allows us to focus on what we're good at, both at an individual level and a macro level. You don't have the knit your own t-shirts or build your own LCD TV, you can buy them at the shopping mall.
However, because we've specialized AWAY from being able to do all of these things for ourselves, we're reliant on a functioning grid to deliver them. If the grid stops working or becomes too expensive to interface with (energy cost, taxes, etc.), then we're screwed.
So, survivalists and preppers seek to reverse the trend of specialization and become self sufficient or grid independent. There are, of course, varying levels of self sufficiency that you can choose to go after--some people are more gung-ho than others. However, you need to realize that self sufficiency is costly and inefficient; specialization exists for a reason. Doing-it-yourself is very expensive, both in terms of investing in your home's infrastructure and in your time.
Let's look at producing your own food, and let me start by saying that I think growing your own food is a great idea. First thing you need is land; 2 to 5 acres, at least. If you're living near a population center (jobs), this can be a considerable expense. You also need all of the farming implements--tools, machines, watering systems and so on. Fertilizer, seeds, sprays and weed killers. And then lots and lots of labor. Planting, watering, weeding, caring for and harvesting. All of this labor has an opportunity cost--you could be doing something else with your time - like working at a job.
Do the math. How much does your family spend on food in a month? $400? $600? Even just looking at labor costs and ignoring all of the machinery, cost of land, seeds, etc., and figuring that you would need to work 4 hours a day (this is the time figure given in the Backyard Food Production DVD), and your farming time could otherwise be spent working a $12/hour job...your effective cost of food producing labor would be:
$12 x 4 hours a day x 7 days a week (no breaks for farmers) x 4 weeks = $1,344 a month
And yes, I know there are other benefits to producing your own food (peace of mind, quality, health and so on), but regardless, you can see the cost and inefficiency here, just when looking at labor! Add in land, cost of production, machines and the numbers become even more skewed. And it's with a $12/hour job!
This same inefficiency will run through everything you would want to be self sufficient in. Want to generate your own power? You'll need massive investments in equipment--solar panels, windmills, diesel generators and tanks, etc.--plus labor (operation and maintenance), spares, operating costs, learning time, and so on. Doing it yourself is costly and inefficient when compared to just hooking into the grid.
Am I trying to discourage anyone from becoming less grid-dependent? No, not at all. I am just trying to point out the rarely discussed costs of becoming more self sufficient. Before venturing into a self sufficiency project or lifestyle change, crunch the numbers. Calculate the costs, both in terms of real costs and opportunity costs. Figure out the gap between those self sufficiency costs and the cost of being grid tied. Then decide if your reasons for becoming self sufficient in that area are worth that sizable gap.