In a related question @Harper wrote the following:
Note that airport car rentals will NOT permit you to drive off paved roads, literally paved roads, read the contract!
In addition, @PeterM mentions the following:
While you may get away with it, if anything at all happens to the car the rental companies will do their utmost to make the the renter take full liability. This includes things that could happen though no fault of the driver. In addition in the US at least there have been rental car companies that have installed GPS trackers in their cars, so the company could know where you have been no matter how well you attempt lie about it.
So what are the practical implications in the following scenarios:
- You drive on the unpaved road with no damage to the car
- Your car is damaged sometime after you've visited the unpaved road - say from an accident on a regular highway
- Your car is damaged directly on the unpaved road
For an example of a popular unpaved road, see Mauna Kea on Big Island in Hawaii which is visited by tens of thousands of tourists per year in their rental cars. "Practical" in this question refers to how much money you will lose by visiting the unpaved road.