I only have one commute bike with a rack and that's my steel Bianchi Advantage, yet I commute using more than one bike. I use the one with rack and pannier whenever I need to carry a lot of stuff--towels, clothes, shoes, shopping for groceries, which might be once a week. The rest of the time I will choose one of the other bikes without a rack, be it carbon, aluminum, or vintage racing steel. These are much more fun to ride, especially without panniers.