Here, the main use of "above ECON" speed is at ATC request to make the inbound flow work better. It might cost a bit of fuel but will mean that I will not mess around possibly 5 aircraft behind me. Optimally, you'd clear the 250/10k before Top of Descent. If you can't, there are still benefits for all involved.
Originally Posted by 152
With CI 30 giving a 270 kts idle descent and CI 6 giving 245 kts, one presumes that the earlier TOD and slower idle descent is more efficient in terms of cost.
Only if fuel is expensive... Extra flight time costs money as well.