A tracking number is an alpha-numeric number string assigned to an item for the purpose of tracking. It is very useful for knowing the location of time sensitive deliveries when the corresponding barcode of it is being scanned as an item moves from collection through to delivery.
Many customers use the number to know the transportation process of their stuff. It is developed because it gives the detailed information about the time, route, and current status of the consignment and many people need this. There are many tools even provides both origin courier and destination courier info all in one place. For example, if you shipped a package from USA to China, you can enter USPS TRACKING instead of enter China post and USPS. This is very simple and time saving.