If you look at my timeline, you'll see that I use RunKeeper to track my morning cool down walk, and I have a FitBit that keeps track of my steps. But I DON'T walk to loose weight, and neither should you.
A recent study (here: http://www.ncbi.nlm.nih.gov/pubmed/25353081) shows that if you're walking as exercise without changing your diet (as in: what you eat every day), you will increase your aerobic conditioning, but you're more likely to gain weight than loose it.
So why walk?
Walking (or 30-60 minutes of movement a day) is an indicator for longevity. Those who move more have a tendency to live longer. No, it's not hard and fast, it correlates but it doesn't necessarily cause longer life. The likelihood is that more physically active people have a tendency to take better care of themselves in general.
So, long slow cardio? Basically, not good for weight loss.
What should you do? Weights, body weight exercises and interval training. Well, at least if you want to loose weight anyway.
If you want to gain weight, then keep hitting that elliptical, walking, or going out for a "run" (which, BTW, if you're at 10 minutes a mile, you can get more benefit if you actually just walk because you won't pound your knees and other joints as much).
Of course, I'll end this as I end many conversations about fitness - you can't out exercise a bad diet. Food choices, even putting calories aside, make a huge difference in your health.
Oh, and BTW, just counting calories doesn't work either - but I'll explain that in a different post.
Till then, #BeFierce have #NoGuilt and #BringtheFit