There are two good, but slightly differing explanations for why film should be stored in a refrigerator or freezer.
Kodak's Reason
According to Kodak, unexposed film should be stored at 55 degrees F (13 degrees C) or lower. For longer periods of time, 32 degrees F (0 degrees C). Their reason for this is that heat results in fogging that lowers the speed of the film, flattens contrast, dulls color and adds graininess.
Conventional Wisdom adds that...
It is not so important the film be kept cold but at a consistent temperature. It is the warming up and cooling down that will degrade the quality of your film over time. Keeping your film in a refrigerator prevents temperature fluctuations.
Storage and Care
Never heat film that has been chilled. Never leave film out in the sun or next to a heater.
Always let your film sit out and naturally warm up to room temperature after storage. If you attempt to load the camera with the chilled film, you run the risk of having condensation spot your film. Also, emulsion and base of cold film contract at different rates, possibly causing film to jam in the camera.
Although it isn't a good idea to shoot film that has been stored for long periods of time, it can be done. Film is a perishable product that ages, but how long it is good for is debatable. The magical deadline is supposed to be six months. I could not tell the difference in graininess, latitude or color in Kodak 7297 after six months storage in a refrigerator. However, the cinematographer that shot it claimed he could. I came upon a number of rolls of film that had been in storage in a refrigerator for up to six years. I shot three test rolls, one of each stock. The Kodak 7222 B&W Negative was crisp and clean after six years. At five years, the Kodak 7248 Color Negative was a bit grainier than usual but otherwise usable. The Kodak 7293 Color Negative stock, also five years old, was unacceptably grainy but still had decent color reproduction. Unless you are going for an experimental look or have a lot of the stock, I wouldn't recommend trying to use old film stock without a thorough test shoot. The lab should be able to test for increased fog levels (a sign that the film is old) upon developing.
Exposed film should be developed as soon as possible. The exposed footage is the sum total of all your work and the longer you wait to send it to the lab, the better chance you have of accidentally exposing it or it becoming damaged by heat or humidity. The film is especially vulnerable now that the original seals have been broken. Seal your film cans carefully with masking tape