It looks like the data app is a collection of dashboards, but is there any advantage besides grouping them? The docs say they are independent so if I create a data app with a dashboard in it and edit either dashboard later the other dashboard wont be changed. Is there anything to gain from creating a data app?
Data apps are collections of linked dashboards that create a curated, application-like experience. It also allows you to link between dashboards with Facets. That way you can navigate between the pages in the app and maintain the filtering or facets applied in the original page.
For example, you could link a faceted list of most-active users to another dashboard. Clicking a username in the first dashboard opens the linked dashboard and filters it to show only metrics from that user account.