Like all insurance/warrantees the company selling them pays out (on average) less in coverage than it collects in fees/premiums otherwise they would go out of business. So, they are good in situations where the most expensive thing they would ever cover would be more than you could pay yourself, otherwise you are better off being self-insured.

For healthcare or vehicle liability the chance of an extremely expensive event that could bankrupt you is a lot higher than for a car repair. For things like home or car warrantee you will generally be better off just putting the money you would have paid for the warrantee into a savings account and pay for repairs yourself as they arise.

Yes, there is the occasional situation where every appliance in your house dies in a short period of time and the warrantee works out but there are a lot more people who get little or no benefit from the warrantee. If there weren't then the companies could not make a profit selling them.