The reason for the long period of refrigeration is mainly for flavor. Although the activity of the yeast slows down during refrigeration, it is still alive and produces alcohol and other byproducts of fermentation. Also, there is bacteria (e.g., lactobacillus) that also continue to function during refrigeration and produce a wide range of acids and other compounds that contribute to the flavor of the finished crust. You can usually smell a lot of those fermentation byproducts.
Refrigeration of dough also allows you to control when you want to use the dough. Most doughs will hold during refrigeration for about 48 hours and, in some cases, as long as 3 or 4 days, but you have to be sure that there is enough sugar in the dough to go out beyond 48 hours. The yeast continues to feed on the sugar all that time.