What happens to MythTV files in LMCE DB once Myth removes them?

I was just having a look around the Files and Media section of the web admin and went over the tv_shows_* folders to see what was up. When I checked show missing files, I got a whack of stuff in the database but no longer on disk.

MythTV will purge recorded shows as required, and I see a lot of entries for stuff that it has deleted or I have deleted through the MythWeb Recorded Shows web page.

We watch TV through the system all the time in the living-room, and the tv_shows_* folder on that box naturally contains a whack of database entries for shows we have watched. Myth has since expired them and there are far too many to delete by hand one by one.

So my question is... what happens to those entries in the database? does it matter that they are in there taking up space?

Is there an easy way to clean that up within LMCE?