As a Swede living abroad this creates a headache when going back. When combined with swish needs a phone number but to get a phone number you need to have a registered address, etc.
Presumably they have cards they can bring with them on the trip that work in Sweden even though their address is outside Sweden?
I know when I travel abroad I just take and use my normal cards without a problem.
For cards, depends on the bank. I know my bank at-least do send the card abroad to my current home and as long as i keep my digital authenticator ID (bank ID) i am able to access that, renew cards. Do most banking services etc.
I also managed to get a new bank authenticator by going to the embassy and get signed papers etc, however it took about 5 months or so if you don't have any cash that might become a issue. :)
Plus of course any time you need to give money to an actual person and not a business.