So it is really about what kind of deductible you will have vs. what you pay for it.

If I save 100 EUR 10 times renting a car and I expect to have one damage costing me 1000 EUR every 10 times I rent a car - it is neutral EV.

If you can't afford the "hit" of a large deductible if an accident happes, then it would make sense to pay more here and now to reduce or eliminate that risk.

I have saved thousands of euros over the years by electing to go with the included insurance, which typically is around 1000-1500EUR deductible, if I remember correctly.

So if I crash my rental car the next three times I rent a car and have to pay 3x1000EUR deductible, I will still be in the green.

Last time I picked an upgraded insurace, it was because we were a group that rented together, and I didn't want to risk friendsships over who might have dented the car etc. :)