[Christ]

THE person was referring to dfco, wherein fuel is cut when certain conditions are met. It is not universally applicable.

Its efficiency depends alot on the skill of the operator.

Considering that using gears to decel, or hold speed, case by case, is basically the norm for driving instruction, even in automatics, and these transmissions don't have abnormal wear/failure patterns, Id chance a bet that you're not doing anything harmful, and your friend is probably regurgitating something he heard out of context, in an attempt to sound like he has some knowledge on the subject.