Factorio Forums

When you select to craft an item a temporary request is made in the logistics request if there are not enough items in your inventory for the missing items. It attempts to find the fully completed needed materials, or at minimum, smaller values, such as instead of getting the needed gears as it cant find them, it instead gets the amount of plates needed. Why? Well it would be helpful sometimes if you can't hold all of the needed materials for a large machine, such as a reactor or a modded item.