As a German living in the UK i currently juggle two SIM cards, and whenever I fly back home I have to mess with the data flatrate there since it's worth activating the monthly flatrate plan even if I just use it for a day. And then I have to make sure that I don't forget to cancel the flatrate when I leave again. Not to mention that this means I have two phone numbers, and I'm not reachable on at least one of them all the time.