Could it be so that you can shortcut in the expected order (left to right)?
Left associative:
a && b && c = (a && b) && c which means going into a && b, which means going into a, and if it is False, then going up in the expression tree.
If it is right associative:
a && b && c = a && (b && c), which means going into a, and if it is False, you are done.
If you have a conjunction of n booleans, the complexity of evaluating this expression is linear with respect to the position of the first False (in the case of &&). In the left-associative case, it is linear in the number of &&s.
Just a guess. But you got me interested now.
Does anyone have the real explanation?
Cheers,
Ivan