Depends. My direct one-way commute is about 4mi/6km. Most mornings I will ride from my house, drop my backpack with my lunch and office clothes, do an interval set or meet a buddy for a training ride, and then back to the office, shower, change, be presentable at my desk. On those days I'm wearing bibs, jersey, and whatever other necessary warmers, vest, gloves, etc. And then in the evening, I will usually just ride straight home in my office clothes. I won't even bother changing my shoes since my SPD-SL road pedals work fine as platforms for a short ride (as long as you're wearing rubber soled shoes). The only special equipment necessary for that is a velcro band to keep my pant cuffs out of the chain. (And that's not even necessary, since I could just tuck them into my socks.)
During the cool season (say from Nov. to March), I can also ride to work in my office clothes if it's dry and I'm not taking a training ride detour. If it's raining I prefer not to get my office clothes soaked. In the summer, it can already be over 80 at 8 am, and I will be soaked from sweat even from a short mellow ride.