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 Split per-vertex normals.
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.
Using this option permanently alters any UV maps applied to geometry. The plug-in properly re-assigns the UVs to the newly split geometry. There is a limitation in regards to UVs, when importing this geometry into an empty Maya scene, using the Combine per-vertex Normals option in the FBX Importer, as it may result in incorrect UV assignments.
