I can imagine that MODX may open session but in PHP8.1 and MODX 2.8.5 it is throwing PHP warning: session_write_close(): Failed to write session data using user defined save handler. (session.save_path: /tmp/sessions)
It’s a best practice to call that before an exit() to make sure sessions are written and closed.
If it is executed when no session is opened it can cause a warning (previously in PHP7 that was just a notice) and if you’re sure you will not run it from anywhere that has a session, you can safely remove it. To give an example, the import script can be run from a snippet so that may have an active session.