The "Refresh Remote Dashboards", which is only available for dashboards shared through a sharing link, allows you to refresh shared dashboards from inside Geckoboard's user interface so that you don't have to reload them manually.
This is particularly handy, when you are displaying dashboards on several devices and/or on devices that don't have a keyboard permanently connected.
This way, when you edit a dashboard i.e. upload a new custom CSS file, you don't have to go through every device displaying that dashboard to make sure changes are visible everywhere, instead you can simply go to that dashboard's "Dashboard settings" and use the "Refresh" button. All devices displaying the dashboard will show its latest changes.