ManualDoc:W192

You may want to group the suppliers of a certain type of products within the same category,
in order for you to compare the purchase prices your company got from them in relation to the same type of products.

Or you may want to group the customers located in your country within the same category, a different one than the one which groups the customers located abroad,
in order for you to compare national and foreign sales figures.

All of the above is possible due to the fact that Business Partner Group" is a dimension of Purchase and Sales Reports.
To learn more visit Procurement Analysis Tools and Sales Analysis Tools

Finally, it is also import for you to take into account that each business partner category allows you to setup a different set of ledger accounts to be used while posting transactions
such as customer receivables or vendor liabilities.
To learn more about it, visit Accounting tab below.