Originally Posted by aeropix

Back in the 1990's Northwest Airlines had an experimental program for fuel saving across the pacific. They would shut down one (or two I can't remember) engine bleeds and one of the Packs (Air conditioners) during cruise. I remember riding jumpseat on a few of those flights with a friend of mine. The pilots specially briefed the cabin crew that they would be shutting down the pack and to call the cockpit if it got too "stuffy" in the back. Well, that was the old smoking days on the Tokyo Run so this program failed miserably, predictably, and quickly. After one summer trial, the air was not switched off any more!

In any event, this was back on the old 747-200 with a flight engineer that had a bit more granular control over these systems. On today's aircraft this would not be possible, as the air systems are all computer optimized. So the bottom line is there is no "boosting" nor "starving" of the air supplies. It's running all the time regardless.