Originally Posted by Chris Scott
Tipsy Barossa’s other point refers to the difficulty of adding a burst of extra thrust to what the A/THR is providing, but which the throttle levers − parked in the CLB detent − are not reflecting. This facility was not available in the early days, and I’m not keen on it.
... and for good reasons Chris :
This strange procedure came up only in 2004 I believe (?) through a FCOM BULLETIN :
AIRCRAFT HANDLING IN FINAL APPROACH
Above 100 feet
The purpose is to reduce the A/THR response time. This will temporarily deactivate and arm the A/THR.
"This possibility should be used in exceptional circumstances, and should not become a routine flying technique."
Below 100 feet
The story is different too, and can get pretty interesting ...
Overall, many agree that it is much more simple to be in manual thrust by 1000 feet and forget about this mascarade.