Comment by decimalenough

Depends very much on the country. Many countries don't care, some like Japan will absolutely refuse to let you drive a car without one.

And it has to be the correct flavor of IDP too, meaning proper 1949 Geneva Convention on proper 1940s cardboard, none of that new-fangled 1969 Vienna Convention nonsense. Oh, your country has signed up to 1969 but not 1949? No car in Japan for you then.