This tag is controversial, and at this time there is no direct evidence of Microsoft implementing Smart Tags, but this could change, and webmasters need to be aware of them. Essentially, some Microsoft products including Internet Explorer could in the future be configured to provide definitions or links to other information related to the content of your website. In a worst case scenario, your outbound links could be replaced by Microsoft links, or your SEO optimised website hijacked by Microsoft and their advertisers.
Selecting Yes to this tag will prevent Microsoft products from using Smart Tags.