Hello,
After running Apache Bench, making 100k requests, I note that disk consumption increased by more than 100 GB. I believe that this is caused by file-based session files. When does LS purge these files, and where are these files precisely stored on disk?
Thanks!

That depends on your php settings and is not controlled by LimeSurvey.
Default value is 24 minutes. And the location of the filebased sessionfiles depends on the settings in php.ini too.