I would have thought that a tanto would have been a back up piece for a samurai engaged in combat and would have been used to penetrate the soft spots in a target, such as between armor plates or under armpits and inside elbows, where one could find and sever arteries and such. Would have worked well in a locked close in combat.
I have seen tests where even the traditional rounded tanto point was proven to penetrate tough materials with less resistance than a clip or spear point and they also said that the wounds would have been more severe and life threatening due to the penetration of a larger cross section of blade. More like the sucking chest wound of a gunshot, less likely to close up and clot.
But I guess it is all subjective now adays, there is not much real history on the subject.