Supplier tax - Transaction level in Company tax control

What is the functionality of the Supplier tax - transaction level check box in Company/Tax control tab?

Help text and the F1 documentation say,

“ If this check box is selected and if the purchase part, purchase charge type or the no-part order line is taxable, it is required to enter tax on purchase transactions (e.g., purchase order part line, charge line, no-part order line).  Also it is required to enter tax on supplier invoices (e.g., manual supplier invoices, preliminary supplier invoices, external supplier invoices)”.

“Transaction level, validate the tax code on each transaction row.”

Is it validated in the PO line level and in the supplier invoice? Does that mean the application does not allow to enter a PO line in a PO without a tax code in the line?