ArcGIS Open Data allows you to expose the data that you already have in the ArcGIS Platform (be it ArcGIS Online or on ArcGIS for Server) to the hungry Open Data consumers that are out there, without extraneous exports or transformations that you have to maintain.
With ArcGIS Open Data being a public facing site, you can get some usage reporting benefits from the ArcGIS Activity Dashboard. For more detailed usage reporting, you can integrate the Google Analytics with your ArcGIS Open Data site. This can help you understand how people are finding your site, what items are they searching for, what city are they from, who is on the site right now, what browsers/devices do they use, how long are they spending on the site, etc.
The following video shows you how you can integrate Google Analytics into your ArcGIS Open Data site.