Best Practices for using "Pay UnMatched Voucher" vs Match Override

What is the proper use or intended use of using the feature pay unmatched vouchers and match override? When should each be used?

It appears that users have a need to pay a vouchers un-matched. The voucher is in match error (Receipt not found or Voucher qty > PO Qty). They do not override the match error. Instead they pay unmatched. The voucher is never matched and then the PO gets closed. Now the match error is "Invalid PO Status". AP_Match continues to try to match these vouchers. I have old vouchers going back many years that AP_Match keeps trying to match. My thinking is they should really override the match error instead of opting to pay unmatched.