3D Effects are a gimmick used to sell the Nintendo 3DS. This gimmick was known to cause eye problems in the eyes of young children (it's uncommon though). Its counterpart, the Nintendo2DS, did not have this gimmick (hence the name).
Games[]
It was used as an optional gimmick for Mario Kart 7 and players of the Nintendo 3DS were able to use it (this obviously doesn't apply to the Nintendo 2DS, it's has this name for a reason).