This is known as the "warm way" although it probably makes no difference to
temperature.  I use it all the time although my boxes (British national) are
square so there is no long side. It has the handling advantages Frank
mentions.  Also there is a tendency for bees to store honey towards the rear
of the brood box and have the brood towards the front.  In summer this makes
it easier to find the queen.

In winter the stores are in one block that they can chomp through.  There is
thus marginally less chance of them sufferrng isolation starvation  when they
have eaten all the stores on one side of the box and it is too cold for them
to move across to the stores on the other side.

Chris