Reduced thrust T/O's and climbs consume extra fuel. Generally with jets, lower RPM = less efficiency. The savings are presumably derived on the maintenance side, with reduced engine wear. One confidently assumes the bean-counters have figured the cost of the extra fuel to be more than offset by increased engine life
bunyip - I believe that the actual peak EGT attained in the cycle is the most important factor in the possible savings, ie slightly lower temp is beneficial even tho' for a longer time. That would be why there is little engine-condition related benefit to reducing below climb thrust. Same for cold Wxx T/O's, where cruise EGT at altitude may match that at T/O anyway.
quid - Many operator's are now justifying reduced thrust for noise reasons (usually climbing initially with a significant post-T/O thrust reduction). While this does lengthen the footprint, the overall noise level is lowered noticably, presumably to an acceptable level for those additional people exposed to it. Sort of like moving gently thru' the gears on a motorcycle takes it further down the street to top gear than full bore acceleration, but maybe lets the neighbors sleep none-the-less
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Cheers, Atlas