AFAIK the shorter one was used in closer quarters, including indoors. Seppuku involved a dagger, for the doer, and the long sword for his assistant, for the decapitation.
42 posted on 09/15/2009 8:33:47 AM PDT by Lucius Cornelius Sulla
("men of intemperate minds cannot be free. Their passions forge their fetters." -- Edmund Burke)