If you don't mind a non-pro asking a question...
Do any companies require pilots to fly manually on the line on any kind of regular basis for precisely the reason Alpagueur320 gives? Or is it entirely at the captain's discretion? Could you always fly with automatics with obvious exception of take-off and disconnect for landing?
Also, if the throttles do not move on the Airbus when the A/T is engaged, when you disconnect them does N1 not "jump" to the thrust indicated by the manual position of the levers? Hope that question makes sense.
Our Ops Manual (UK low cost) says that you should make full use of the automatics where apropriate but equally should maintain manual flying skills.
To disconnect the autothrust on an airbus you can either line up the thrust lever position indicator with the curent thrust and then disconnect or else close the thrust levers (this will disconnect the autothrust) and then put them quickly to the desired thrust position before the engines have a chance to spool down.