What does this Op Amp Circuit in the Voltage Regulation Section Do?
It looks like it discharges the 12 volt rail capacitors when the input power is disconnected. When input power reduces to 0 volts (or drops significantly) the comparator output switches to 0 volts. This turns off Q2 and biases on the clamping MOSFET. This discharges the 12 volt output capacitors. If the input supply voltage has only partially dropped, the circuit won't fully discharge the capacitors.

I have no idea what the function is, but that's what it appears to do.