This thread probably belongs in Technical Talk section, but UVs extending past the border is often used for tileable textures. The Coordinates just continue tiling outside of 0-1 space, it is also why you can offset overlapping UVs for baking purposes and still have them work.
I am pretty confused. I thought in order for a game engine to read textures correctly they needed to be in the 0 to 1 space on the uv sheet. This guy made a texture atlas and they extend the border. How would this work in engine? What am I missing? Skip to 10:00 and check it out. I understand if it was for a render it…