I usually work three or four days each week on the sixth floor of a building, and I usually take the stairs, which keeps my glutes firm and works my hamstrings. Not to mention my lungs. Walking makes me feel good, I enjoy it, but I won't delude myself about it making much difference in my weight.
Just look at the math:
I weigh in (happily) at about 110 pounds.
At 4 mph or 15 minutes per mile (a good "brisk walk" pace) I only burn about 62 calories each mile.
It takes burning 3500 calories to lose a pound.
(uh-oh, I see where this is headed)
At 62 calories/mile that works out to just under 56 and a half miles. To lose one pound.
So for me to lose about ten pounds (from walking alone) I would need to walk the equivalent of from Boston to Richmond, VA, Denver to Salt Lake City or Omaha, Portland (Oregon) to Sacramento or Missoula, or from New York City to Toledo, Ohio.
Of course, everyone's mileage varies. If someone weighed 220 pounds, they'd only have to walk from Pittsburgh to Cincinnati to lose ten.
I don't think walking a little farther in the mall or food store parking lot is gonna make that happen. It can make me feel like I'm doing the right thing on a number of levels, but it won't burn off much weight.