if you get low on energy/slow and you want to add power faster,
with autothrust you can go momentarely forward of the climb detent. this will give a increase thrust faster then waiting for the autothrust, especially in gusty conditions when the headwindcomponent changes constant, this in turn will change the "grounspeedmini"
above mentioned proc is mentioned in the fcoms 3.04.70p2 for the a330
s.