On the 330 some (myself included) will push for managed descent (thus giving v/s-1000 initially) 2 or 3 miles before calculated descent point. Giving smoother push over, and smaller power/pressurisation variations. Difference in fuel? So insignificant that anyone questioning it probably needs to get out a tad more. Have looked at the fuel estimate figures for the next WPT pre, and post maneouvre, never shows any variance, for what thats worth.