The way I think about it is that insurance always favors the insurance company (or they wouldn't do it). So statistically you should only insure things you either have to (full coverage on a car with a lien), or things you can't afford to replace (your home, your health in an expensive-case scenario). I dropped collision from my plan when the car was paid off and I could afford to buy a new one if I totaled it. I don't have a car anymore but I carry comprehensive (no collision) on my motorcycle only because I park it on the street in a high traffic area (car and pedestrian) and worry about vandalism or a bad parallel parker.
And like BlueMR2 said, sometimes there's an emotional piece of mind benefit. If you'll sleep/drive more soundly having it, and it's not derailing your financial plans, it can still be worth it. If you drive a mustachian car to begin with, they're really not that expensive to insure in most areas.