I have never been to Turkey but I have always gotten the license when I rented a car in a foreign country. They never asked for it 10 years back but I noticed the last two times I rented a car, once in Greece and last year in Costa Rico, the rental agency asked to see it. So I would get one to preclude any problems.

You actually answered your own question. i cannot see how an international permit, which is just a piece of paper can be helpful when the law does not require it!!

We rented cars from several rental companies in Turkey and nobody ever asked to see the International Drivers Permit.
In some Asian countries, car rental companies cannot do business with you if you don't have that piece of paper.

I take an IDP everywhere the cops are likely to speak anything other than English. (Otherwise how do they know you are showing them a driver's license rather than a Michigan - or wherever - library or state park card?)

nytraveler, you have a poor view of cops everywhere. For example, the Turkish drivers license actually writes "Drivers License" on it in English also, so that the Turkish cops are familiar with the words.

I have rented cars with a Turkish drivers license in the unted States, italy, France, Spain, Germany, United Kingdom and never had any problems in the past 25 years. i do remember needing an IDP in the 1970's in Europe.

I drove for two weeks in Turkey; Ephesus, Pamukkale, Fethiye, Antalya and points in between. The drive from Fethiye to Antalya is spectacular. I used my US license with no problem. Roads were generally good and traffic not to difficult at all compared to may places we have been. I did not drive in Istanbul but the traffic there looked no worse than most European cities and not as bad as London, Rome and Paris. Getting an IDP would have been pointless.

You do not need an international drivers licence in Turkey, however just for further information police knows the difference between a library card and drivers licence!
Happy travels,
Murat