[Man Eating Duck]

Originally Posted by holymadness

I don't want to clutter my hard drive with older versions of epubs; is there a way to return to the previous behaviour? Did I uncheck a preference by mistake?

P.S. If there's any way to batch remove the original_epubs via Calibre, would someone be so kind as to let me know? Thank you.

Try to set the two tweaks to False in Preferences -> Tweaks (at the bottom), "original" in search for tweak (see attached screenshot).

To remove all instances of ORIGINAL_EPUB from your books *please* make a backup of your library first... Done?

Then: select all your books, right click -> Remove books -> Remove files of a specific format from selected books. Select the format ORIGINAL_EPUB.

Edit: Ninja'd by DoctorOhh
As he mentions, the original format is kept for a reason. If you remove it, make sure that you have the original file somewhere else. Replacing covers is probably safe, but for instance epub->epub conversion can be destructive in non-intuitive ways.