International Drivers License -- Do you really need one?

I think I have seen this debated here before but not for a couple of
years.

Are there any countries where you MUST have an International Drivers
License?

Has anybody had a situation where they had to show it to somebody who
would not accept their home drivers license?

Last I recall of the debate was that Nobody had first hand experience
of actually needing one but several people had heard of somebody who
knew somebody that actually had to produce it.

The other conclusion from the debate seemed to be that they are
relatively cheap and easy to get so why wouldn't you just get one?
Even if you never need it. That same arguement could probably be made
for a dog license even if you don't have a dog.

So, what is the current concensus and experience?

We will be driving in Germany, Czech Rep, Slovakia, Slovenia, Poland,
Hungary Croatia, Italy, Austria, France at least.

Gord