Use sub-customers when you want to enforce a hierarchical relationship between customers. Sub-customers can represent many things:
You can choose to bill either the sub-customer or the parent.
A sub-customer's transactions always appear in the sub-customer's own account history and in the account history of its parent(s).
On the Customers page, open balances for sub-customers are included in the balance of the parent(s).
You can have an unlimited number of sub-customers, but you can create sub-customers nested only to five levels deep, including the first customer.