In most circumstances it does save fuel. Takeoff thrust is typically at N speed above Optimum Thrust Specific Fuel Consumption (TSFC), thus any reduction to or towards Optimum TSFC N will use less fuel per unit of thrust produced.
Even if the thrust reduction is below optimum TSFC N, you should still save fuel even though TSFC is now worsening again, as the rate of TSFC degredation for engine speed increments below optimum is significantly less than for increments above optimum.
A lot of "It all depends" in this one, it all depends upon your specific engine characteristics. The reply above is generic.
Last edited by Old Smokey; 16th Jul 2012 at 07:56.