I think Patrick means an optional “Delete source file after successful conversion” setting.
For example, converting track.flac to track.aac would create the new file with the correct extension, then delete the original only after successful conversion. If conversion fails, the original should remain untouched.
However, this would also need to update references in the Music Library and playlists. Otherwise, they would still point to the deleted source file.
So the useful feature would be “Replace original with converted file”: convert safely, update the references, then remove the original. This would be especially helpful for batch conversions.