GPS allows significantly more crop to be grown on the same land. By giving plants the ideal spacing they harvest the amount of light they need without shading each other or letting light fall unused on the ground (or on weeds that in turn shade the plants). GPS also starts/stops each row of your planter as you cross already planted areas of the field, thus saving a lot of seed and in turn leaving more land free to grow crop instead of seed. GPS also always fertilizer to be placed where needed thus not over fertilizing some areas while under fertilizing others.