I would guess that CCX is referring to 'Doppel Duty', because iirc he and Pandaroc were tied for the best time stating that there's no room for improvement left, so when I later played that level I was surprised that beat their time without even trying hard. I've got particle effects disabled (actually in the hope to stop the screen shaking when other players go super nova in MP, but in vain), so that seems to kinda make sense.
I actually think it's applicable to any level where there's clones left that you cannot rescue and that don't get killed on their own either, but the level only quits once there's no clones left on the map.
EDIT: I think it also has an effect on exiting normally (i.e. level quits once the last clone has entered), as can be seen here:
http://clonesgame.com/level/digitoughIt makes a difference of 0.28 seconds.