By DOM access I assume they mean that since background pages are pages, you can do things like use IMG and SCRIPT tags to load resources, and perhaps a CANVAS t

By DOM access I assume they mean that since background pages are pages, you can do things like use IMG and SCRIPT tags to load resources, and perhaps a CANVAS to rasterize images that you then serve to pages via an extension URL or something. I've done stuff like that before so I can imagine there being use cases for it, but it's kind of niche.