Okay, there's some truth to it. You plan the menus, go to the grocery store once that week (or two weeks), buy what you need, and stick to the plan. That's definitely more frugal than running to the store repeatedly or going out to eat.
But I developed an even cheaper way. I was shocked recently to see my scheme promoted on a website for eating local and organic.
Plan your menu AFTER shopping, not before. This allows you to stay on budget because you aren’t shopping for special ingredients to make pre-planned meals. You can take advantage of the best deals and plan your meals around those. This can also help by keeping those unplanned budget purchases from going to waste in your crisper drawer while you carry on with your planned menu.
I like to jot down meal-plan ideas as I'm going through the store. Lettuce is cheap? Grab a few heads, write "taco salad" in the margin of your grocery list, and then make sure you grab a tomato and a pepper to be part of the salad.
Find some pork roast marked down to a frugal price because tomorrow is its expiration date? Toss the roast in the cart, make a note of it in the margin, and remind yourself that it should be cooked tonight or tomorrow.
Find the el-cheapo deals at the store and then figure out what you'll turn it into. It doesn't always work: sometimes you can't find the fabulous deals. Other weeks, time constraints at dinner will trump the plans you could've developed from the week's good deals at the store. But other weeks, everything falls into place easily ... and for half the price of pre-planned menus.