[Koha] Why three levels in ACQ (Order, Basket. Basket group) ?

Hi to all, I'm trying to understand in deep the ACQ modules. For me now is not clear why there are three levels (Order, Basket. Basket group). I don't' understand well the use of Basket group. The manual is not very clear on this point. Cheers Zeno Tajoli -- Dr. Zeno Tajoli Dipartimento Gestione delle Informazioni e della Conoscenza z.tajoli@cineca.it fax +39 02 2135520 CINECA - Sede operativa di Segrate