I started bike commuting for health (and economic) reasons.

I used to weigh something like 210lbs and for someone that is only 5' 7" thats a lot. I changed offices about 5 years ago to one that was only 5 miles from home. So I started getting the bus. The wife then spotted an old wreck of a bike for sale so I got it and a helmet and started cycling once a week, then twice a week until I was doing it every day.

I'm now a lot lighter (about 180 but have been as low as 163lbs) and I still enjoy commuting.