The Sears salesman asked if we wanted one on our air conditioner in 1971. My wife worked in the home office of Sears and we knew they were pure profit for Sears and a very expensive insurance policy for us. We havn't bought any for anything in the last 30 years, and I can't remember ever being burned by that choice.
Point is... 1) They have been around for a long time as a vehicle to build retailer margins. (not a bad thing to a retailer!) 2) Don't ever purchase them! Save the money and bet on black if you ever reach Las Vegas. The returns are better... Regards, Bob S.