Re: The question is, are there any sites making legitimate use of this?
This is just one of a whole suite of "interventions" backed by the "Web Incubator Community Group", which is part of the World Wide Web Consortium (W3C). Such tweaks are intended to become part of the standard, although the relevant standards aren't controlled by the W3C.
This particular change has been under discussion for two years with multiple attempts at implementation. And even this version only hits the beta channel on the next Chrome update.