Sometimes you can get a discounted rate by buying the CDW at booking rather than waiting at the counter. And since it is required, I suggest doing it online at booking to avoid any language confusion later.
What is optional is the Super CDW that covers the deductible on the standard (and required in Italy) CDW. Your own insurance or credit card MIGHT cover that but you need to be really sure.
Personally, when renting a car outside the US or Canada, I like to get the Super CDW. Yes it is expensive and mostly profit for the rental agency. But the reporting and documentation requirements are very stringent to get your CC or insurance to cover you and you can't always rely on getting what you need and trying to follow up later might be near impossible. And it avoids any scams by the rental agency to charge you for "damage" that just so happens to be the same cost as the CDW deductible. And you get to rest easy that a minor mistake on your part (and very easily someone else's part) won't cost you a thing.