In my opinion, it's something you can easily do without. There is a "sweet spot", so to speak, where you want to hit the shot with power but can't quite reach it (and you can never hit with much power using the bridge). That's when an extender is handy and I think these situations come up about one shot every 4 games or so.
I have a Tony Ryan and it doesn't hurt the cue but it won't fit in my case (a Justis). So I leave it at home and use the bridge. The Justa-Bridge won't fit in the case either, by the way.