Usually a texture file is a square image : 512x512, 1024x1024, 2048x2048, etc…
There is no problem with that … but suppose you want to texture for NWN 2 a model from another game. And in this game the texture of the face is in one file
And the texture of the skull and neck or some part you wish to keep in another (in my example I wanted the earrings)
You can try to reorganize the file that includes the face, but it’s a lot o work, especially when you are not an artist !
There is another way … combine the two texture in a rectangular file. In my example I had two 512x512 textures. I Upgraded them to two 1024 x 1024 files, and combined them in a 2048 x 1024 file.
Thus I was able to create the back skull texture from the face texture. This allowed me to have no difference where the face and skull connect, and I was able to include some details.
This method is very accurate when you import in NWN2 a building from another game or from DAZ. Buildings often come with multi tetxures created per materials. HAving non-square texture files allow you to combine the various textures without too much scaling, cutting, or other manipulations.
PS : The idea came from an Assassin’s Creed texture. This was the first time I saw a non-square texture file.