Boeing throttle position is directly related to engine power, whether manual or automatic. You can hear and see the servos controlling the throttle position. Autothrottle is used for automatic landings, though in the event of unserviceability, manual thrust can be used throughout. Autothrottle is never encouraged for manual flying as you can end up with confusing pitch/power couplings as the autothrottle can respond peculiarly and you can end up fighting in pitch. However, some airlines like to use autothrottle in standby on final approach as a safety aid, and it will intervene if speed falls excessively, and will be available for TOGA. Although Boeing don't recommend this, I think is is good practice.