I wondered about this. I would have assumed it would be an opt in function.

Will need to talk to my bank as they have moved my ATM card over to a Visa Debit (I did not ask for it) and I have no idea which account the Visa part links to. I have 2 accounts on that card and I don't want a transaction failing due it accessing the wrong account. Might need to do a 'test' one day and see what account it hits.