When creating pixel art, one can work on a high-resolution version of the image (e.g. 500x500), then downsample it (for example to 100x100), and then continue the work in the downsampled version.

In some cases, it's good to try modifications of the high-resolution version and see how that affects the final result. In other words, to have a smooth workflow of non-destructive editing.

So we need a layer that (down)scales the image. All layers before it are 500x500, all layers after it are 100x100.

Shifting 500x500 layers in front of this "scaling layer", or shifting 100x100 layers behind the "scaling layer" would require scaling the contents of those layers. Such shifting can be disabled in early versions, or achieved by "scaling filters" and/or "scaling masks" in later versions.