ASER, to paraphrase (slightly) George Orwell: "all FADEC systems are equal, but some are more equal than others!"
The throttles behave more or less like standard Speed Select Levers (SSL) in normal operation. You press START, and then set the throtle to IDLE and the engine auto starts and sets IDLE Ng (about 67%), however this is not enough to keep the Nr out of the lower Nr/Np avoid band (36-49%) so you manually set 'about' 70% Ng with the throttle to set Nr/Np to 50-55% to stay out of the upper avoid band of 56-67% Nr/Np (necessary for carrying out the MGB BYPASS test). Then you advance the Throttle(s) to FLY, Np governing takes over and you have 105% set. Scheduling limits Tq to 30% max if you are heavy handed with advancing.
Once in FLY, if you retard the throttles, the Nr will decrease, just like a normal SSL. So, on the face of it you have greater control than with a simple switch arrangement. However, there is no direct mechanical linkage, so in the event of a dual FADEC channel failure, the engine shuts down, and in the event of a fixed power failure, you have no control of the engine.
I suppose there could be a back up system, but that just so
Provencal 