That being said, on Airbus you are supposed to keep your hand on the thrust levers as well as on Boeing and you can "help" the autothrust in any moment
I don't know about the Airbus, but to "help" the autothrottles is frowned upon by Boeing 737 series. In fact, Boeing published a bulletin many years ago warning crews not to apply pressure to the throttles with AT engaged as any pressure more than a certain figure (I don't recall the psi) can damage the clutch motors in each throttle.
This mostly happens when selecting TOGA and misguided PM's urge the throttles forward with their hand behind the levers as a backing up policy when there is no need since they won't slip back because of the internal throttle friction system.
Like those pilots that "follow through" on the flight controls while the other pilot is PF, there is nothing more annoying for the pilot to be smoothly opening the throttles manually and feel the other eager beaver pushing them from behind. In fact, something goes wrong and the PF suddenly whips the throttles to idle to abort and the PM still has his hand behind the levers as a following through habit, severe hand damage has happened when the PM's his hand is jammed between the throttle and the top of the start levers because he can't remove it in time. . I have seen it happen in the simulator and it is very very painful.