From Scientific American: Are fat bums a sign of good health?
Harvard Medical School has done studies showing that having a "pear-shape," with fat on the thighs and butt, might actually be helpful in preventing diabetes 2. Subcutaneous fat is a layer of fat everyone has right under the skin (it also helps keep you warm). The bad type of body fat is visceral fat, which accumulates in the abdomen between organs and gives that beer belly.
Like it says in the article, not all fat is bad.