Honestly, I was never really a fan of them. While some could make it interesting, most times it was just pointless filler for the reasons stated (saving money, an actor being absent during the time, etc). I usually just skip those episodes.

And with the shows today, that's not really common (and I think stopped being used as much a while ago), and I would be pissed if it happened now considered the shorter seasons we're currently getting and they wasted it all on a clip episode.