Hello @isNaN
Document Server stores files in cache indeed, but clearing them manually can cause various issues related to the document opening. By default Document Server performs cache clearing once in 24 hours (more details about process of cleaning I’ve posted here).
services.CoAuthoring.expire.files is a lifetime of a file in cache that was successfully edited and saved back to the storage. However, the Document Server does not delete such files immediately after the lifetime end. It does that on a schedule set in services.CoAuthoring.expire.filesCron. So, by default, at 12 am each day the Document Server will check if there are files in its cache that are 24 hours (or more) old and delete them.
If you want, you can change the cron job timings according to your needs to make files in cache being remove more frequently. I’d suggest sticking to this approach, because, as I mentioned before, manual removal of items in cache may cause serious problems with the integration.