I noticed that if my tile size is 254 then OSD starts out loading images at a sensible level (level 9). However if my tile size is 1024 then OSD starts all the way down at level zero and loads all levels up from there. Is this to be expected? I don't see why it needs 0/0_0.jpeg given that it's 1x1 pixel.
GPUs sometimes require power of 2 textures, so if you're just over (e.g. 1026) they have to pad it into the next bigger power of 2. OSD uses canvas, which presumably involves the GPU on at least some browser/OS combinations, so it may be relevant for performance in those situations.
...but I don't know for sure. At any rate, it's easy to do, so it's okay if it's a "just in case"