All the time... when you get to 60 at least. Don't worry about it too much before then, but I'd use it (if only to practice with it). Since I lvled Bard before the potency changes (AKA right as HW was released...) I can't give you much info there but I did keep it on pretty much all the time after I got Empyreal Arrow.
It's DEFINITELY worth it; people just don't want to use it and thus claim it's useless.