That's actually incorrect. Rental companies might require you in the fine print to bring an IDP and some states mandate that you carry your home licence along with an IDP.

To be honest, it's much more convenient to have it with you. Doesn't cost a fortune and any officer stopping you will understand the licence. I've seen plenty of people in the US being confused by the new driving permit used by EU countries, that come with little to non description of the numbers that are printed on them.

BTW: You didn't say that you booked already...