Security Theatre or threat to kill?

I can't understand the point of sending fighter jets up to "escort" a passenger plane under bomb threat. Is this just security theatre - which comes at the risk of an exploding passenger plane also knocking out the airforce planes flying so close to it? Or is it an implicit threat to knock the plane out of the sky as a "lesser of two evils", if the passenger plane seems a threat to a large urban population (or tall building)? What realistic help can a fighter jet provide to the passengers or crew of a commercial flight with a bomb on board?