With technical extension concept, you can logically enhance billable items by linking to entries in customer tables. This could be any type of data, e.g. industry specific data like usage data in utilities or high tech industry.
Use technical extension, e.g. if the structure of your customer data is more complex and you like to link data from a set of customer table to a billable item. Or you may reduce redundancy and link to customer data via technical extension instead of storing same data in multiple billable items.
Please find details as follows: