Stagger Penalty Weapons?

What, if anything, is the purpose of weapons with a stagger penalty? So much of the combat strategy in this game revolves around staggering enemies. Heck, the whole trilogy. I see this listed primarily on wand and magic staff type weapons. But while I might like a little extra magic power, it doesn't seem worth the trade off of spells contributing less to staggering of foes. Especially when there are quite a few enemies that take almost no damage until you stagger them.

I think the penalty might have something to do with the amount of time decay the stagger wave decreases if you don't keep the wave up. IGN would have more info in their LR guide.