As a rule of thumb to decide whether to get any insurance (which a warranty is).
Insurance companies on average charge you at least twice the amount of your actual risk.
So, only take insurance if one of two conditions are true
- You cannot afford the financial impact if something happens.
- OR you are reasonably sure that you have a higher risk than 75% of other insurees.
Examples of type I: catastrophical healthcare, fire insurance, liability, flood, kidnap & ransom ..
Examples of type II: living in a bad neighborhood with recent plague of car thefts (auto insurance), a pyromaniac is roaming the area (fire insurance). Or what REWahoo gives as an example.
Warranties for household appliances are a waste of money. I've seen profit margins of 80% and higher on them.