TYPO3 Core

If a user adds a video (e.g. YouTube) to a content element and places that in the folder "foo".

Then you clear the processed files in the Install tool and use another user that has no access at all to the folder "foo" (e.g. outside folder mounts),
accessing the page using the page module or editing the content element will result in an exception.

The reason is that the online media helpers use getContents (to retrieve the online media ID) on the .youtube file which calls assureFileReadPermission()
when retrieving the corresponding preview image.