Also, one of the main benefits of using free days in the U.S, (one-way rentals) doesn't really apply overseas. Most one-way rentals outside the US charge a reasonable per day fee, however tack on a distance based drop fee that the free day will not apply to. Some places are reasonable on one way drop fees, like Germany, while others are ridiculous, like Australia.

As the other poster mentioned, most one-ways are only allowed between corporate owned locations overseas, and often times your rental will be serviced by someone else. (I.E. Enterprise in Europe or Redspot in Australia). Obviously might be worth it to redeem a free day though, especially for high demand expensive periods.

On another note, Emerald Club benefits don't really apply to overseas rentals. (Other than possibly having a pre-printed contract) This also means the highest car class you can redeem free days for as an Executive Elite varies by country, so you'll have to check each country on a case by case basis. There are several countries around the world where free days can't be redeemed at all. If there are corporate Enterprise locations in the countries you're looking to rent in, the better the chance that the redemption of Emerald Club free days will be allowed.