Personally, I refuse to have carpeting in my home; but, that is whole 'nother story.
Carpet pads really do cut down on the wear and tear of carpeting. These pads come between the carpet and flooring of the home. All flooring structures are hard; whether, it be concrete, hardwood, or whatever. Despite the amount of vacuuming done by anyone, sand/grit will eventually work its way through your carpet onto the structure or padding below. As you walk, the grit will rub against the subflooring and whatever is on top of it OR between the pad and the carpeting. The underside damage done to the carpet by the grit is lessened if the carpet rubs against a soft, smooth surface rather than a hard one like cement.
The damage done to the underside of your carpet wears out your carpet just as fast as damage from the top.