Not everybody has Insight, and even Meditation can't always keep up with high-level Vengeance. (Speaking from experience.)
I usually shoot for level 4-6 Holy Shield at first so I'm not recasting it every time I turn around, then pump it further at the very end once my main skill is built-up enough for my tastes.
I usually shoot for level 4-6 Holy Shield at first so I'm not recasting it every time I turn around, then pump it further at the very end once my main skill is built-up enough for my tastes.