How/when does Unreal clean out the Automation Transient Directory?

I recently stumbled onto the path for the Automation Transient Directory:

Given the description I assumed that assets in that directory would be cleaned out whenever unreal starts up, but this is not the case.
This led me to believe that I need to ‘run’ something else, like an automation function, or event. I’ve only uncovered dead ends in my attempts to find the answer.

Any info on this is appreciated.