Activate this option to combine geometry vertex Normals.
Common uses of this option include reverting the Split per-vertex Normals option of the FBX Export window. For more information regarding this workflow see .
When you use the Combine per-vertex Normals option in the FBX Importer, the Maya FBX Plug-in performs the inverse operation of the Split per-vertex Normals option in the FBX Export window. This can result in incorrect UV texture maps (see the note below).
If you are not using a merge-back workflow (merging FBX into an 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.