For the pedants, assuming your airline has done the analysis and considered the fuel related costs and time related costs, moving away from the official CI in either direction, will increase the total cost of the trip...thats the point.
Once in the descent, the burn is the same regardless of speed...have a look at the FF and see if there is an appreciable difference dependent on speed...
If you arrive at TOD with a certain amount of energy, you've got a choice about how you dissapate it.
The difference between idle descent and stabilised final approach FF on the 73 Classic is ~2400kg/hr...from memory. Thats about 40kg/min.
Therefore if your thrust levers are coming up more than 2.5 mins i.e., ~7nm prior to the 1000 AAL gate, you've just cost yourself >100kg of fuel...
My guess is that is where the extra burn derives its origin from as I know very few pilots who, even when given the opportunity, can consistently arrange their descent with such precision.
Maybe the EZY skipper concerned was trying to?
I have to say, as a crew we've stabilised below 500 RA, filled in the paperwork and still have jobs...