If you have dark leather couch, you should oil it down with castor oil at least once a year to prevent drying and cracking. This works for all kinds of leather goods, including jackets. Put a toothpaste sized line on the cushion, and rub it in with your hands. Like a baseball glove.
If you have light leather, you should use petroleum jelly, not castor oil, as castor oil darkens leather, but can give a cool antique-ish look.