Pros:
1. More awake and alert at the end of the commute.
2. Depending on the route, commuting can be more leisurely and relaxing (I used to ride home along the canal towpath on summer afternoons)
3. Don't have to worry about parking.
4. The commute is combined with exercise- gym membership is unnecessary and time is not wasted at the gym.
4a. If you didn't go to the gym previously, you can lose weight without cutting down on food (or eat more without gaining weight)
5. Save money on fuel/public transport fares.
6. Heavy traffic is less of a problem.

Cons:
1. Have to plan more for the weather conditions.
2. Finding the motivation to head out in the cold and wet.
3. Carrying lots of stuff can be an issue.
4. Have to deal with occasional blind/incompetent/half-asleep motorists