I am not exactly sure I get it yet, if the image was not power-of-two sized, it wouldn't make a difference for low-end GPU then (since they will consider it like a power of two size still), but will be in theory a smaller filesize at the end, and also:
Square power-of-two guarantees that the GPU texture will also be exactly the size of the spritesheet.
but in that case, the the added texture ins't used either, unless it means the GPU would deteriorate the texture in case of non-power of two, but since 1 frame only objects aren't spritesheeted nor resized, it seeems unlikely to me
Ashley
EDIT: I misread, low end GPU doesn't support at all then, but it is still weird for the non-power of two sized exported for one frame, that they works