80/20 I suppose you don't fly the 737. Sir Donald was refering to a manouver discussed here some time ago:you can 'deselect' the speed,during approach,by pushing the speed button,while flying manually.This way ,the A/t remains armed,and ,pushing TOGA it will command go around power.
In order to avoid mixed flight complications (a/t with manual flight) Boeing recomends complete manual or automatic flight.
The problem that can appear in this particular case is,A/t sensing a decrease in speed,just before flare,and minimum speed protection becoming active,the result being power aplied by the a/t (whic was armed), just about when you intend to start the flare.It can complicate your life a little bit.
I use to deselect speed when expecting a late clearance,and an eventual go around,but as soon as I receive clearance to land,and not bellow 200',I disengage the a/t.
Brgds Alex