Turbineblade
My recollection from several years ago is that the low idle condition is brought about by the system sensing that Flight Idle is not achieved and the system is still in ground idle - several % N1 lower than flight idle. Flight idle allows the engines to spool up much quicker for power/speed demands when on approach primarily. As such, while it is desirable, by disconnecting the A/thr and manually advancing the thrust levers to the flight idle setting, you will still have the (manual) quick spool up required in flight, so the flight is ok to proceed. As I say this is from 737 recollection and by logic - which could be fallable.
Rgds