If you're in Eco mode with DSG in "E" gear selection, you have marginal gains from freewheeling down gradients.
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So...how many people drive theirs in Eco and Normal, then added a pedal box because their throttle response felt dull?
My experience from the daily commute dictates otherwise. Freewheeling gives a small but noticeable mpg improvement and I have never been able to hit such low consumption figures as when I drive in ECO on the same route, same conditions. This (and not the lazier throttle response) is why on the boring slow drives where no real progress can be made I switch to ECO and go on an economy challenge. With a pedal box you cancel out the lazy throttle response too so the drive is still bearable. Let's not forget that throttle response of ECO mode with a pedal box on is miles better than the one of Sport mode!
However, the above is true when you want to drive as economically as possible (ie. always outside of turbo spool). For normal driving with mixed acceleration scenarios the ECO's benefit of coasting is eliminated by a) the lazy throttle response and b) the limited boost available. Not sure how known this is but in ECO mode the ECU limits boost to something like 0.6-0.8bar IIRC (that's on a CS) from the full 1.2 bar on Normal and Sport so in an acceleration scenario you will work the engine longer to get where you want. That would explain the less MPG in ECO than in Normal reported a few posts back, assuming it concerned mixed driving.