99.5% of websites that use this tag - it does nothing. Internet Explorer users don't set their own Compatibility View settings, so we can ignore that. Second, if you're cool enough to be on Microsoft's Compatibility View list, you're cool enough to know that you need an X-UA-Compatible tag and you know what it should be set to.
The problem I have is people blindly copy-pasting this value from whatever HTML5 boilerplate they got it from. I'm going to rephrase this section of the post to make my point more clear.
EDIT: Toned down my phrasing in the article to be more specific about when you can safely remove X-UA-Compatible tags. Yes, there's an argument that it doesn't cost you anything to keep it in there, but there's also arguments for ultra-short head tags (<4 KB) related to TCP windows, which I'll get into in another post.