The reason you want to season your cast iron cookware is that there are a variety of lipids that were used in the manufacturing process. Without this initial layer on each pan's surface, any food cooked inside will stick immediately after pouring whatever you're making into your pan.
Not only does this make your cleanup harder but it also puts off some pretty bad odors into your kitchen. Once properly seasoned, foods such as eggs, butter, and meats won't stick at all when poured onto your pots and pans either before or during cooking.