Effect on ATC
These derated climbs are a headache for ATC. A330's generally want to be up at FL350 to FL390 straight off the deck, but the slow climb rate means that they are in the way of all the other aircraft for a longer period. This may well mean you get interrupted climbs with stop offs at intermediate levels. Planning your climb by the controller is much more difficult as predicting your level at a crossing point with other routes is hard to judge. To be honest it's like watching an L1011 in the old days except they didn't climb so high.