In order to keep the shipping cost down, purchased goods need to be packaged into as few and small packages as possible. Very often this makes it is difficult to know in advance how large the final package will be and how many shipments are needed to transport the customer's goods.
This is a big problem for those web shops who want to show their customers real shipping costs. It is also an unnecessary obstacle when booking freights quickly because it requires constant manual work to choose the right package size.