Well - it started as a weight loss / fitness deal, but it has offered me a lot more than just exercise. I throw myself into my job way too much, and I did not really have any hobbies or interests, so cycling gives me a way to get away from work.
Cycling is so absorbing that when I am out on the bike, I really don't think about that much - which is an awesome relief. I pretty much am watching my cadence, urging myself to pedal faster, and watching for hazards.
I now am starting to challenge myself to ride longer distances, I would love to do a century next summer. Why ? So I can have done one.