Not sure about Airbus, but at my company on the Boeings it is a regular practice to 'guard' the thrust levers on first level off and all subsequent level off's.
Reasons I can think of and have encountered in the sim;
- Windshear
- TCAS RA's
- Thrust lever clutch failure
The thrust lever clutch failure is a favourite in the sim, basically feels like an engine failure at level off as only one thrust lever retards, hence always a good idea to 'guard' the thrust levers.
I wouldn't like to 'guard' the thrust levers in areas of turbulance though, have witnessed a skipper many moons ago on a dash8 do this and ended up firewalling the engines - wasn't very nice experience at all!!!!
Don't know how the Airbus works, but with a sidestick I would have thought it would be even easier to 'guard' thrust levers than on the Boeings, and I would suggest a pretty good thing to do - No???