Is "3 way matching" an integral part of Accounts Payable process? Is there an instance where 3 way matching is not necessary?

The answer is Big YES , in my work history i didn't find any where can't apply it , even in the serivce fields its required as well, as its the concept of AP cycle.

Ofcourse3 way matching is an integral part of AP in order to excircise a strict control and fraudulent practices. There are some instances in which GRN may not be available oru the services are hired on a Payment on Approval (POA) basis. In such circumstances only2way matching is only possible.