I figure downshifting is so you will be in the powerband when you need to accelerate. When I first learned to drive, an old guy (probably my current age) asked "Which costs more to replace, brakes or engine?" He went on to explain that engines are designed for producing power, not drag. Since he was an engineer with a hobby of old Italian cars, I figured he knew what he was talking about. After 2 Alfas, 2 Ducatis and a Vespa I still have a love-hate relationship with all things Italian.