It's that we can't stop the adjustment from being created from within a `PromotionRule` class. So if a store have a bunch of promotions which focus on specific group of items to get a discount here would be a good place to prevent an adjustment from being created if the item is not included in the eligible group of items. I think we also need to keep in mind that other rules might be involved but by making this assumption earlier it might prevent more overhead later I guess.