Hi Akshat,
Purchasing in the PO can only be defaulted from Purchase Requisition, RFQ or other Purchase Order and not from PIR or Material Master.
Purchasing Group from Material Master only defaults during creation of Purchase Requisition and Purchasing Info Record.
RFQs are Maintained for Purchase Org and Purchasing Group Org Levels. If Info Update Indicator is set then Info Records are created with Purchasing Group from RFQ irrespective of Purchasing Group of material Master.
Purchasing Group in Info record helps in Standard Analyses and reports if Info-records or RFQs are maintained by different departments for the similar material or material groups.
Purchasing Group in Info records are more helpful when finding relevant info records for material groups
Regards,
Niranjan