I used to commute a couple times a week during the time in my life when I was also racing. My morning commute was about 12 miles, and I would do that at an easy tempo to keep sweat minimal. I carried my work clothes with me in a backpack. For the ride home, I would change back into bike clothes, and leave the work clothes in the backpack at my desk to take home the next (non-bike) day. My home commute was typically 30+ miles with some sort of focused training intent. Occasionally, I would have my commute route intersect with a fast group ride, and hop in with them as they came by.