For the novice car renter: If you have auto insurance at home that covers you when renting a car, should you pay for that additional liability coverage with the car rental agency? You may wish to consider doing so in a foreign country where the inconvenience factor is high if you are involved in an accident or the car were damaged while parked and you wish to just walk away from the car on return.
But, if you are a good driver and going to a very safe, non-congested, "uncomplicated" part of your home country, you can save on your rental by refusing the additional coverage, coverage that may be duplicating what you already carry.
You may want to check if your credit card company also offers free coverage for your rental car when you charge the rental to their card and what type of coverage it is.
(As with any advice, however, you are responsible for your own decisions so verify this information with your insurance agency and perhaps your attorney in advance to make the best decision FOR YOU.)