Do desert and ice really yield no food, hammers, or commerce? What is their purpose?
Yes, desert and ice really do produce nothing. In fact, if you even try to build a road on them, or any other tile improvement, it will take 25% and 50% longer, respectively. Because of this, desert and ice represent terrain that it not worth improving or using, if one can help it. Try to avoid placing cities in locations where they will not have large quantities of useless terrain.