In a talk with Famitsu, Team ninja boss Yosuke Hayashi has revealed that Dead or Alive: Dimensions on the 3DS will have a better framerate without the 3D effect. Running it with the stereoscopic 3D will slow the game down to around 30 frames a second, while running it normally will play with the usual 60 frames a second.
For a fighting game that makes an important difference. The fact that the 3D can be turned off in such an off hand manner means that there is nothing in the game that needs 3D. For a fighting game that is to be expected, but for other titles I wonder if the 3D is needed at all. We are expected to buy a new handheld for the new technology, but instead it seems it isn't necessary.