Boeing recommends AT use only when the autopilot is engaged.
The autothrottle ARM mode is normally not recommended because its function can be confusing. The primary feature the ARM mode provides is minimum speed protection in the event the airplane slows to minimum manuevering speed. Other features normally associated with the autothrottle, such as gust protection, are NOT provided. The autothrottle ARM mode should not be used with Non-Normal checklists. Some malfunctions that affect manuevering speeds cause the autothrottle to maintain a speed above approach speed.
When using the autothrottle during autoland, position command speed to VREF +5 knots. Sufficient wind and gust protection is available with the autothrottle engaged because the AT is designed to adjust thrust rapidly when the airspeed drops below command speed while reducing slowly when the airspeed exceeds command speed. In turbulence, the result is that average thrust is higher than necessary to maintain command speed. This results in an average speed exceeding command speed.
During sporty landing conditions, my experience is that the most skilled aviators, without exception, prefer to disconnect the Boeing 737 "hunt-o-matic" autothrottle system.
No wonder it is the only autoflight system Boeing will allow to be inoperative for a Cat III autoland.
Bottom line: You squat to pee, you autothrottle to land
