Activate this option to combine geometry vertex Normals.
Common uses of this option include reverting the Split per-vertex Normals option of the FBX exporter, which occurs often with MotionBuilder workflows. Activating this option combines geometry vertex Normals that were Split for surface continuity in MotionBuilder. (You have to do this because of a MotionBuilder limitation.)
When you use the Combine per-vertex Normals option in the FBX Importer, the plug-in performs the inverse operation of the Split per-vertex Normals option of the FBX Exporter. This can result in incorrect UV texture maps, see the note, below.
If you are not using a merge-back workflow (merging FBX into existing scene) this option might result in incorrect UV mapping when you re-import the FBX file into Maya. Import your FBX file into to your original Maya scene to avoid geometry UV issues with split geometry.
