just to clarify, I'm no expert, I'm just regurgitation what I'm reading in my "Road Bike Training" book...
You should eat/drink for recovery purposes so that you'll be able to keep cycling with greater effort more often and sooner between rides by properly refilling your muscle cells with glycogen(which in turn will burn more calories than a poor performance/low-energy workout). With proper recovery you can more easily avoid overexertion and overtraining which will eventually catch up with you and make you miserable on the bike(I can attest, I've been through it..makes you very irritable). I think if you're just doing an easy spin for an hour and only cycling maybe once or twice a week, it's not as necessary than if you're going out daily for an hour or more.
I really hope someone that is more qualified to answer will weigh in on this...it's tough to balance weight loss with proper nutrition for rigorous exercise.
edit: great! I'd say ericqu knows a lot more about this stuff than I do
