On our SQL 2012 Enterprise SSRS instance, the DIR C:\Program Files\Microsoft SQL Server\MSRS11.MSSQLSERVER\Reporting Services\RSTempFiles was filling up our 80 GB C: drive w/ 65 GB of RSFILE_xxxxxxx files
As I researched the issue, I found that this DIR acts a little bit like a SWAP file in Windows.. Large SSRS data requests can house data inside this DIR temporarily. I searched high and low for resolution to clear out this DIR (several files named RSFILE_xxxxxxxx) At least one post suggested you do not touch these files as DELETING them could corrupt your installation.
Anyway, after about 45 mins of research, I returned to view the RSTempFiles directory once again ---- AND all of a sudden, it returned to just a few hundred MB used; the very large files beginning w/ RSFILE_xxxxx were GONE! I believe a CLEANUP process initiated and deleted the large files.
If anyone knows the name of the CLEANUP process and would like to reply to this thread with where it resides and "how to set it's cleanup frequency", it would be helpful.