Or when driving in hilly, mountainous country one might downshift to avoid lugging the engine. If you let the engine choose the shift points, all too often the trans will shift in and out of gears, which causes more wear than, for example, downshifting into 3rd or 4th and leaving it there. I've driven my Camry through the mountains for thousands of miles, and using the shifter in that way is a smart and good option.
Toyota included the sport mode in their setup for people to use in an appropriate manner. Remember, there's really little, if any, difference to the trans if the driver chooses the shift point or the trans makes the choice.