If the veil is thick enough, it can also affect potions. So if you're fighting a prep-heavy character, or someone who quaffs at the first sign of trouble, it might be a nice surprise.. especially since they wouldn't even know the veil had shifted.

But yeah, I'd mostly see doing htat if you're trying to raid (or re-raid against some mage-types and need an edge. Drop a handful of items off with Tahren, then go for it. Could be enough to tip the scales your way.