I have set up a user/usergroup for the purpose of previewing Layouts. The following issue appeared: individual media items do not inherit permissions an so they are not shown in the preview. I have to go one by one in the Media browser and set the permission per individual file.
Global permissions can be set in the settings so that new files are group/public, but what about the old files?
When you assign permissions to an existing layout, you can tick the checkbox to cascade those permissions to all items on that layout (ie all regions, playlists and widgets).
I had ticked the box, but a lot of the content was still not shown. Images that are used in Datasets, tickers, embedded, etc. are not affected, so the permissions on those items have to be manually changed one by one in the Media Library.