Since this is an uncompressed file format, each frame in the animation carries its full weight, so if you have 10 frames of 10k PICTs, you end up with a 100k file to push through the wire. It may be too much to ask viewers to wait for a 100k GIF still image to load, but a 100k GIF animation that begins to play after 40k has loaded is certainly reasonable. Animation should be meaningful, not distracting. Ideally, it should add something to the content of your page. What it definitely should not do is disrupt your reader's concentration with needless chatter.
Splash screens are a good place to use animation.
Animated images can provide just the right amount of pizzazz to attract viewers into your site. But be sure to keep the file size modest. Requiring a lengthy download right at the start of your site will lose all but the most committed viewers. That way your readers can view the animation and then close the window. If you present the animation on the main content page it will interfere with the other page elements.