Well, I go mall walking most mornings before the stores open, and I can attest to its health benefits. I can't do more vigorous, aerobic exercises anymore, but after my cardiac arrest, the cardiologist insisted I exercise and walking was his recommendation. The first time I tried, I could only walk a few feet before I would get winded. Now I do around 5 miles. Not a spectacular achievement for most people, but it is for a couch potato like me. And walking has been beneficial to my heart and related health issues such as diabetes and high blood pressure.
I can also attest to the mental health benefits. Several weeks ago, Ii was going through a stressful, bad time. Walking helped to ease the stress and give me a clear head to make the decisions I needed to make. Really does remove the mental clutter.