If for instance you have a character whose eyes have a specular material that uses an exclusive light group. You can very nicely control the amount on shine without effecting the rest of the character.
Okay, you could seperate the mesh to a different layer to do this, but if you plan on library linking the character this is not ideal.
The problem is that when the character is linked into another scene if you create a new light group in that blend file it will not work.
The Sintel render branch build of blender has an extra button under material light groups called local. This allows local versions of the light group to be used.
Sorry to go on but this is very frustrating!
Has anyone used this and know a work around?