Glad you like it @const 
This workflow is very specific to my needs: I need my unity3D app ( here ) to run fluently ( 20fps mini ) on mid-end smartphones. In Unity3D, the more you have different materials, the slower is you app.
Therefore it is mandatory when you have lots of objects using the same shader but with different textures to pack those textures in a bigger one in a kind of atlas. This way, all objects use one unique material and UV coords do the job.
I’m not sure but i guess things work the same way for Unreal Engine. What is GPU consuming in a 3D scene is the texture fetching from 3D board memory to GPU caches. And the less you invalidate those caches, the faster is the app ( just as for CPU^^ ).
This workflow has no interrest in blender itself as blender can handle multiple material properly and blender is mostly used for still renders, not realtime ones.
However, i heard blender is able to handle texture arrays ( wich as far as i understood is some kind of texture atlas having same size textures ) and UV coordinates. However i never used it as i’m not sure of the Unity3D <—> Blender compatibility on this point. Also I found no example of this beeing used in blender…
Happy blending !