Did you search the forum before asking this question? It has been asked and answered too many times to count. That said, my wife found a very good description of extended service plans a while back (they are not warranties, but rather insurance policies with lots of fine print). They are another form of legalized gambling. The company is betting that nothing breaks that would cause them to pay out more than you paid for the policy; you're betting it will. As in all forms of legalized gambling, the house usually wins. Otherwise, these companies wouldn't be in business or make a profit. We prefer to set money aside regularly (earning interest) and pay for repairs as they come up.
Rob