This device protects your LED system from overheating.
You typically mount these on something that gets hot. Then you wire it in series with the input power going to that item that gets hot. When the item exceeds about 160°, this opens the circuit and turns off the device. Once it cools down, it automatically closes the circuit, turning the item back on.
Most people mount these to the LED heatsinks. That way if a fan fails, something blocks the vent, or just simply gets to hot, this little device will turn everything off, saving you from damaging your items, melting your hood, etc.