Lama: depends on your responsibilities I suppose, oh, and age, and depth of pockets!, and risk taking....
I have had ocassion to claim recently, because of a bad smash I was involved in. Personally, wouldn't be without it. Having said that, the premium is outrageous! But peace of mind.
The clause I claimed under was for 'disability' while recovering. I was off flying for the best part of a year. When one drops to sick pay, the extra insurance provides you with one less worry during the recovery process.
Very common over here (UK) but only with large organisations, I suspect. Stick with reputable companies, that way they won't change the goal posts when they smell a claim coming, but instead honour their commitments.
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Thermal runaway.