There is no simple, magic answer that applies to everyone in all cases.
Much depends on your credit card. I have a card (several, actually) that provide CDW virtually everywhere (haven't tried North Korea or Syria, but definitely works in Italy, Mexico, Ireland, Japan, Morocco, and every other place I've dared to rent a car). Some details may depend on what country you're renting in (every country has their own laws, or course). There are some "gotchas."
But whatever card you want to use, and whatever place you want to use it in, there are two absolute prerequisites:
1) You need to do your homework (with solid, unambiguous information, obtained in writing, from the insurance providers that your credit card uses), and – most important of all...
2) You need to understand all the details of the coverage You need to know what exclusions there are in what's covered (there's always exclusions) and what the limits are (some my be laughable and useless) and what exactly you need to do at the rental counter (eg, you must accept what is legally required, and decline everything that is simply optional which they will try to sell you, and you need to be able to distinguish between the two).
Critical for success: You MUST do all that prep work before you firm up your plans, and long before you show up at the rental counter. Coming off a redeye flight, exhausted, jetlagged, excited, with whining family members waiting on you and a long line of other renters behind you giving you the stinkeye, with people yammering around you in foreign languages, when everything is confusing, stressful and "foreign" is no time or place to be reviewing teeny tiny legalese print on a contract (which is what you will be about to sign). Overlook something, and you could be out of pocket for the costs of a new car, or more (think medical liability). Know your stuff, understand what's coming before you start packing, and all you need to do at the counter is show your plastic and paper, verify a few minor details to ensure they have not changed, sign, initial, and worry about navigating safely.
You can save a ton of money this way (I have). But you absolutely must have your head in the game, and do the planning in advance. If you can't/won't/choose not to (a perfectly valid choice, BTW, and for some folks the smart choice) then just pay what they're asking for full coverage and be done with it.
Caveat: Even with full coverage, it's smart to know the limitations and exclusions - you may be surprised. I was surprised to discover (buried deep in the fine print) that my AutoEurope rental agreement prohibited taking the car on a ferry (tip: you can get that exclusion waived, if you ask beforehand, but I wouldn't expect any success asking at the rental counter).
Good luck and happy motoring.