I would like to have your expert comments / links that PO approval rights for Direct / Indirect material should be with Finance or Purchase department.
Here is my view & request to advise further - PO process is linked with buyer then it should be with Purchase; however Finance team can be added for approver during PIR as per release strategy. But ultimately it should be with Purchase team sine they knows better negotiation & terms / condition with supplier.
Also I understand its business call PO release strategy can be finance & purchase both but would like to have common views on same.
As you mentioned, its business decision based on the manual of authority of the company!
If you expect Finance team in the approval for non-stock items, I hope its to ensure the correct cost objects. However, if you have Funds Management with proper budget control and proper authorization controls, the finance approval shall be replaced. You may check the option.