Just had an interesting conversation with an old friend of mine who is a relatively new mom. She was talking about how she's using weekly meal planning to lose her baby weight. It'll help keep her from eating out so often, and ensure she has good ingredients on hand. For my part, I started doing it to save time and energy thinking about what to cook for the evening meal. I've also used it to lower food expenses and minimize waste.
In short, it seems like the ultimate purpose for planning is to CUT BACK on something. Might be calories, dollars, time, or trash, but for those of us that do it, it's about "slenderizing" elsewhere.
I recall seeing a weekly menu listed on the fridge calendar where I was babysitting as a 15-year-old. I concluded this woman must be nuts, or at a minimum obsessive-compulsive. I made sure the toys were all put away just so that night. Now I recognize that she was tapping into what busy parents do in their households all the time—organizing a bit so there's more time for other things.