Mxsmanic wrote:
Is there any reason to drain fuel tanks in any way other than
symmetrically in normal flight? I notice that most aircraft have
complex controls for fuel flow from the tanks, and I wonder if there
are things one is suppposed to do during normal flight, or if this is
just to provide for possible equipment failures or a need to shift the
center of gravity of the aircraft in an emergency.

Because you need to find the fuel. Some planes have a "both" selector
but not all are set up where that would work. Also, for twins you need
to be able to transfer the fuel out of the tank from the dead engine
into the good engine since the good engine burns more fuel when its
working by itself.

-Robert