combine SAP/BI and SAP/CRM

Hello,

i have a question about SAP/BI and SAP/CRM. I actually don't understand why a costumer need a BI-Module to expand his CRM. I know that the combination from these two Moduls are an analytical CRM, but where are the difference, where is the benefit? Could someone give me some background information why it´s necessary or useful?

thanks for your help.

Regards, Peter