It will prevent the speaker from too over high power output may speaker damaged it use transistor and relay cut off as safe.
This is the Class G 300 watt MOSFET Power amplifier circuit with PCB MOSFET. It have more feature, maximum RMS output power: 200 watts at load 8 ohms or 360 watts at the load 4 ohms.
High power mosfet amplifier circuit ideas, the sound is very aggressive, as compared to transistors and ICs,can be low-high-frequency response,
2 Circuits of High power transistor amplifier circuits, 200 watts and 300 watts RMS