Chromecast App doesn't work with Group Speakers

@bobbyD or @gopher.ny regarding

and " * ChromeCast integration: settings to enable connection keep-alive through device polling."
could some advise what the settings (no documentation) do on the app page, eg what is getting polled? why the option to very the poll interval? and whether we now still need to initialise GH speakers frequently (eg Chromecast helper)