If you import non-deformed geometry, the normals are locked on import to Maya. These locked normals can create problems when you deform the geometry in Maya.
For example, if you import blend shape targets that were created in 3ds Max and then export them to FBX, they import into Maya with their normals locked.
You can address this problem if you unlock the deformed object's normals in Maya. To unlock the normals, import the geometry into Maya and then select Normals > Unlock normals.
When normals are locked by Maya, they will not move with the geometry when you deform the imported objects. If you do not unlock these normals, you may experience shading issues when you apply modifiers such as skin or blendshapes.