Sam,

That code is how the bank decides what to put on the description line in the vendor's bank statement. So for example, a client pays me by EFT through the bank and my vendor profile in AP is set up as 460-Accounts Payable. When I look at my online banking, I see their deposit as "Accounts Payable" followed by their company name. So it might be useful in telling the person doing the bank recs where the money came from and what it's for. However, if you're setting the client up to email payment advice, it shouldn't really be a concern what option you pick.