Anyone who has played Sid Meier’s Civilization or Age of Empires, will know all about the importance of resources. They determine what you can build, trade or sustain. Wars are fought over them: I know I’m guilty of this, taking out the French (in Civilization) for daring to set up a village and steal the gold resource I had been eying with lust.
For these reasons, writers need to know what resources each of the countries or regions in their world are privy to; after all, resources determine what is possibility and are a great way to provide a sense of realism. Resources can also add a good source of conflict in your story.
How plentiful or sparse certain resources are will have an effect on your story. If your story takes place in a desert, your characters are not going to have access to wood products, unless they are imported. The lack of wood will affect tools or weapons used by your characters, similar to countries with less access to certain metals. Consider how the people in each country or region cope with not having certain resources.
Import and export is another important aspect, and these concepts can say a lot about characters if they own certain products that are made from rare or inaccessible resources in their country.
Take time when plotting your resources, research where they are found to make sure where you want to place them makes it logical. Think long and hard on the impact of certain resources being rare or absent and how people have adapted to not having them. Do resources provide conflict within your world? Which resources or products made from them are costly to import? How do resources affect your world’s economies?