I bike to work in a relatively hopeless attempt to not be the lanterne rouge of the Bike Forum Commuters Club on Strava.
Bike Forums Commuters | Strava Club
Other than that: it's fun, saves gas, simplifies transportation schedules in my 1-car household, and I've been losing weight. Normal reasons. It's also nice to do something other than driving to work as that's what I do at work too and I think it's a good lesson for my 3 year-old who comes with me a lot of places.