T D
A pedantic point; FADEC computes what the engines are going to do in response to the Flight Guidance / Thrust Management computation.
In this sense moving - following up - thrust levers are a comfort blanket.
The all important need is for situation awareness - understanding; this requires human integration of present and future flight path, including thrust required, which requires a comprehensive instrument scan.
Situational awareness is the ability to know what is happening around you and to anticipate what might happen next. It’s the mental discipline that keeps you alert, prepared, and ready to act without hesitation
.… means knowing what “normal” looks like so you can identify deviations.
… a tactical skill that is not just about knowing what is going on. It’s about staying engaged and thinking critically to respond effectively to both routine and unexpected events.
https://safetyrisk.net/situational-awareness/
As for manual flight - 'when
are you allowed to …'
When ever the pilot chooses to do so. The pilot is in command and should act as situations require; you cannot fly by referring to a book.