Brian Watson wrote:

This got me thinking literally, "are there any depots or
strategically-placed triangular junctions at which a train could be
turned right round?"

LU trains are not, as far as I know, biased to be driven from one end
or the other,

But you can't necessarily couple the north end of one train to the south end
of another identical train, unless the original trains were facing the same
way as each other.

but I could see circumstances such as the Circle Line
where it could be an advantage to turn a train to even out wear on
the wheels.

There are no such facilities in depots. The two obvious triangular junctions
which can turn a train are visible on the tube map near Gloucester Road and
Aldgate. There is a non-obvious one linking Moor Park, Croxley and
Rickmansworth. The two obvious loops for turning trains are shown on the map
at Heathrow and Leytonstone-Hainault-Woodford, and the non-obvious one is at
Kennington, allowing trains from Goodge Street to head back to Goodge Street
without reversing. Trains cannot be turned on the Bakerloo, Victoria,
Jubilee, or East London Line without a significant trip on another line, and
trains cannot be turned on the Waterloo & City without being lifted by
crane.