In this article https://support.plex.tv/articles/213095317-creating-optimized-versions/#:~:text=Unwatched%20Only,part%20of%20the%20optimization%20job
Unwatched Only
Choose whether or not the optimization should apply only to items that have not been watched. If this option is selected, then once an item has become “watched” it will no longer be part of the optimization job.
In case there are several users using the plex server, does it wait for everybody to watch before removing or does it remove it after one person watched it?