visualeditor-dialog-meta-settings-index-help says "You can force search engines to list this page in their relevant results, or force them to not do so."
I don't think this is an accurate description. A page on a private or offline wiki can't be listed in a search engine no matter what the setting is. If a search engine doesn't choose to list the page, then adding this tag can't force them to change their policies. On the other side, if a search engine disregards robots.txt and similar controls, then you also can't really force them to ignore the page.
Maybe this should say something like "You can mark this page for listing in search engine results, or request that it not be listed".
Also, is it possible for this statement to indicate the default for the namespace? Then it would say something like "You can mark this page for listing in search engine results, or request that it not be listed. The default is $1", where $1 is something like "all pages listed" or "all pages not listed".