Personally, I don't think it makes much difference. The airlines use estimates for the weight of passengers and baggage. The only items that the airlines know the weight of are the empty plane, fuel load, freight and mail. These items make up the majority of the aircraft's weight.
You were asked to move because of the center of gravity (CG). The airline doesn't know the exact CG locations of the baggage, freight, or passengers. "Towards the back of the plane" is such a general criteria that leaves a large uncertainty about the center of gravity of these moved passengers.
My wife and I were asked to move from first class to coach (we were non-revs) on an AA
767-200 flight departing ORD
. The passenger load was much lower than planned for weight and balance (due to misconnecting passengers). As we were taxing to the active runway, the F/A asked us to move back to "anywhere in coach". The length of the coach section meant that moving within coach would have more impact on the CG than moving from the last row of First to the front of coach.
Anyway we moved back to coach as we taxiied. Then two minutes after takeoff, still in a steep climb, the flight attendant had us move back up to first, even though the seat belt sign was on and we were in a steep climb.
[Edited 2004-05-08 16:05:14]
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.