VAT System setting for supplier

When setting up a supplier, if we edit the company (see first image below), an « Accounting Situation » window pops up (second image below).

There is a « VAT System » setting with three options: i) blank, ii) Common System, iii) Option on delivery. (see the image below)

What do these three option settings do? Do they control the tax for purchases from this supplier? If yes, how?
Thank you for your attention