Bonus Buy

Dear Gurus,

In IMG under SD - Basic Fuctions, we have 'Bonus Buy'. How can we use this?

Normally in R/3, I am told, we are not able to use Bonus Buy, then what is this for??

If possible plz give 1 or 2 example of Bonus Buys that can be done in our R/3.

Thanks and regards

Venkat - Hyd