Hey Alexander. That's the location that Tableau Server stores data extracts associated with Workbooks and Data Sources. The date is as old as it says presumably because someone published something that is backed by an extract, but it's not set up to frequently refresh (or to refresh at all). So if you start deleting old files out of here, you'll start breaking people's workbooks and / or datasources.
Older versions of the same extract get automatically cleaned up after the extract is refreshed. You really shouldn't need to be doing anything manual with these files.
If you're concerned about space, I recommend starting to periodically review the content on Server for size and how often it's used, then having people start cleaning up stuff that doesn't meet the bar.
Thanks Matt for the clarification.
On Thu, Jan 7, 2016 at 2:12 PM, Matt Coles <