Italy too due to fire codes. I would expect Singapore, Russia, China, etc. to be strict about seeing passports that match the names on the reservation.

BTW I would read the T&C to say that any extra person charge for the second guest (at properties where rates are different for single versus double rooms) will be covered, but not for additional people beyond two, regardless of whether an extra bed is required or not. [Hotels don't want to encourage people packing into rooms for free nights.]