But considering that CSS1 allows authors to specify a non-scrolling background as a single image, a row of images, or a column of images, there may be presentations in which an animated background could be used to good effect. An animated GIF takes up less bandwidth than alternatives that might be used to achieve a similar effect.
Content can be more than reference material or technical FAQs.
I've seen provocative web pages of animated art and poetry in which the emotional content is very much dependent on the effects. And there are surely instances where a simple animation is more illuminating than many words. One way or another, all content must be presented to be understood.