Having reached the CI computed TOD point and started your descent, if you choose to adjust the speeds, what happens to the total burn from that point on?
Then you are deviating from your plan. No reason though why you shouldn't manually insert a manual mach/ias (for known speed requirements etc) prior to TOD if speed control is expected in the descent. That may well save you from being forced to alter your speed in a descent to comply with ATC requirements - thereby trashing your profile if you didn't plan for it prior to TOD.
End of the day, Plan the flight sensibly/practically and try to fly the plan. Of course I agree that total cost is important (though the tree huggers might argue wrt tankering which saves money but burns extra fuel) but I was responding to a specific question/comment about fuel burn, not total cost.
Min fuel burn = max time at idle thrust in descent!
