For parcel shippers, pick-to-carton logic uses item dimensions/weights to select the shipping carton prior to the order picking process. Items are then picked directly into the shipping carton. When picking is complete, dunnage is added and the carton sealed eliminating a formal packing operation. This logic works best when picking/packing products with similar size/ weight characteristics. In operations with a very diverse product mix it's much more difficult to get this type of logic to work effectively.