They're everywhere. Part of a trend that just won't die. Slide shows that load automatically and then distract you by automatically flipping between content, just a bit too fast for you to be able to read it.
Why do designers do this? Because they think that users are okay with automatic movement on a page? Because their clients are determined to pack more information into less space, instead of editing down their text? Because designers feel they need to maximize the possibilities of multimedia?
Yeah, all those things. All mistakes.
Here's an unusual mistake to make, though: putting a video clip that auto-plays inside a slide show that auto-switches, so that by the time the video starts playing, it's out of view. You have to navigate through the slides to pause the video. That's an amazing mistake to see on the 'net, especially on such a prominent site.
I don't know if there is a place for slideshows on the 'net. I think so. I think it should just be for content that is sequential, though. And there has to be some compelling reason for it to be in a slideshow instead of just as a series of normal paragraphs and words.
There also has to be some very easy and obvious way to move between slides. And the thing shouldn't automatically switch from one slide to another.
I think at this point, they're a requirement on any site. They've become part of what's expected, not by actual web users, but by clients and designers. I continually get asked to create them, and I continually refuse, because I don't want to be responsible for dragging my clients into the past via their websites. I also don't want their front pages to take longer to load than they need to, and loading content that's not immediately visible does sabotage that effort.