If you have a blog or profile page, and music or a video automatically plays, that’s not just annoying, that’s rude. You don’t know from where users are accessing your site – at the least, you are slowing their access to your very page. At worst, you have some awful song blare from their speakers and draw attention to them.
It’s not just amateurs I’m aiming this at. There are lots of sites hungry for every advertising dollar they can get, and throwing up all sorts of ads to get my attention. They’ve got it, alright: I’m not clicking one ad on their site, and RSS feeds are many times blissfully free of such crap.