I guess we both have some nits...
Your foot has to be somewhere, assumedly it is not over the brake pedal. I feel that if the foot is on the accelerator, deceleration begins immediately (remove foot) when a situation comes to your attention that something needs to be done; during that same timeframe, the CC is still adding fuel before the brake pedal is touched. Milliseconds--microseconds--whatever.
If going downhill, probably it is a wash, since the CC is not adding fuel; but if going uphill, I just think the time needed to defuel would take longer.
I use the CC alot when in open spaces with little traffic. Can't in hills, as the Ford CC will downshift when it senses speed loss and mash on the throttle. Maybe its better in Dodges and GMs.
And, as webslave said above, I can out MPG my CC anytime I want to--but sure is nice to rest the foot occasionally.
'05 36TK3 Mobile Suites
'10 F450 new to me
'09 F450 Lariat 4x4--died