pax2908
It is more economical in fuel terms to use max take-off power followed by maxclimb power until reaching optimum econ cruise level. (You achieve your econ level earlier and therefore spend longer at that level)
However the additional maintenance costs at max rated power far outweigh any fuel cost savings; for now anyway.
There may come a point where the cost of fuel could increase to such an extent that it would be more economic to use max power settings - such a fuel price hike would need to be quite significant I'm given to understand before this was the case.
It is interesting that from a 'global warming perspective' none of the green lobby appear to have latched on to this one. If they did they would then probably claim that airlines were destroying our environment in order to save cash whilst totally ignoring the additional load on the environment by the production of 'hot end' parts for gas turbines.
Regards
Exeng