It is not necessary to consider departments as outright cost centres.
Some companies adopt a different approach when treating cost centres.
[6] For example, by considering a call centre as an independent unit, the firm can calculate how much it is spending each year for its call centre support service.
If a cost centre is not considered independent then it would take a lot of effort in measuring the cost of providing this service because it will include dividing up the company's entire personnel and phone bills by department each month.
Furthermore, the main objective of a cost centre is to minimise cost whereas the main objective of a profit centre is to maximise profit.