In theory they are preparing for a possible step off, thus avoiding trapping the leg between ground and machine. They know they are near to the limit.......

The old story of the air brake similar to flaps on an areoplane can also be considered. They are presenting a low level brake triangulation into the air stream which assists stability into a corner, Just sitting up raises the centre of gravity.

Finally, doing this leg out may be to relieve a wedgy caused by the acceleration and braking at high speed. (B***s Out !)

Otherwise it is just an affectation..............

Professor TT Fannenbergenstein