From what I understand, as the plane reaches a certain speed, the ones with inboard and outboard ailerons, the outboard ailerons lock into position and the plane is completely controlled by the inboard ailerons. The flapping motion you see on approach is the inboard ailerons reacting to the manuevers the pilot is making with the stick. If you look closely, at slower speeds, the outboard and inboard ailerons work together.
Anyway, think about it...balance a pencil or a rod on the top of your finger, it takes more energy to tilt the rod to the left or right if the pressure is being applied closely to the finger the rod is balanced on. Now, move your finger one end of the rod, either left or right, and you will find it takes less energy to tilt the rod. It's all about leverage. When the plane is at cruising speed, using the inboard ailerons gives the pilot a less-sensitive, smoother banking methods.
However, inboard and outboard ailerons are not on all aircraft. In the Boeing line, the 727, 747, 767, and 777 all have inboard and outboard ailerons. (Not sure about the 707). The DC-10, and MD
-11 have both as does the L-1011. AFAIK, NONE of the airbus products have inboard ailerons except for the A300/310 you show in your picture.
Hope you can understand what I wrote. It's hard to explain, and it's late, so I'm sure I made absolutely no sense whatsoever.
[Edited 2004-09-06 08:00:40]
"Bangkok Tower, United 890 Heavy. Bangkok Tower, United 890 Heavy.....Okay, fine, we'll just turn 190 and Visual Our Way