One reason would be to free the starter if it jams in the ring gear teeth.
> On my '71 GT-6 starter motor there is a square on the end of the armature
> (end opposite of the flywheel engagement). What is the purpose of this
> why would I want to use a wrench to rotate the armature? I am considering
> cutting the protruding square off (shaft protrudes about 3/8 in. out of the
> of the starter motor) to gain a bit more clearance to the headers.