With the advent of online shopping, most merchandisers release(usually by email) upon finalizing every online order, a tracking number for the customer to trace/track their impending parcel containing their particular purchases.
I feel that it serves 3 purposes:
First, it gives the customer the name of the shipper/courier that will send us our parcel.
Second, it gives the customer an idea as to when their parcel will arrive and will plan their day ahead of time. It eliminates the aspect of the unknown as to when the parcel will be shipped to them as well as its impending arrival. If necessary, one might need to delegate someone to sign and receive the package on your behalf. In some cases, one might have to inform the shipper/courier about this so that it can be noted under special instructions.
Third, it eliminates time and effort on the merchandiser to track the parcel for the customer.
I really consider parcel tracking numbers as a god-send in my opinion.
Just food for thought!