Polyswitches offer very low internal resistance and can react very quickly to overloads which can damage your speakers. Once the polyswitch has been overloaded the internal resistance goes infinite, preventing your speaker or device from being overpowered. The polyswitch devices are reset automatically once the device has cooled.
AUDIO TIP: Want to keep playing and protecting. Put a resistor of 15 ohms or higher in parallel with your polyswitch. Once your polyswitch has tripped the current will flow through the resistor allowing your speaker to play at a lower protected level.