Why can additional work be charged at an hourly rate, especially for large orders?

Additional expenses include the working hours, especially for large-scale orders, for data review, coordination of production, sorting, intermediate storage, compiling and filling the printed products in folders or plan boxes and labeling them, as well as final inspection and preparation for delivery. Additional expenses will be charged in addition to the printing costs resulting from the number of pieces and the unit price. Additional expenses may also be charged if the order processing of even simpler orders takes an unusually long time.