So one reason I was always making thumbnails is that it makes it very easy to refer to treat the thumbnails directory as a cache. Otherwise, it's harder to determine whether I've already loaded an identical embedded image for the album. I suppose I could do the same de-duplication logic I use when creating real thumbnails, but I'm not sure that's really saving us a lot.

However, it does make sense that we'd want to make thumbnails for very large external album art (e.g. folder.jpg files).