So sorry , it's because of short question.. !!!!
The point is, why the AP, FD, A/THR can't use while Main vital system still available??
ELAC1, SEC1, FAC1, MCDU, FCU1 -> Flight computer can operate normally.
G HYD, Y HYD, some of B HYD -> Still normal.
Navigation still operate.
Most system still operate in main function. -> Aircraft can fly normally... (only fly)
Why the AIRBUS have to downgrade or disable AP, FD, A/THR?
The AP, FD, A/THR can reduce work load dramatically !!!!!