Thanks for all the inputs. So basically there seems to be 3 major usages:

(1) Offensive canon fodder - as a free meat pad. Send them as the first wave of impact to reduce casaulties.

(2) Offensive shock reserve - as a penetrating reinforcement to rout the enemy as fast as posible.

(3) Defensive cavalry charge sponge - as the absorber of an enemy cavalry charge.

All of them seems reasonable to me. I use to remember that people think wardog to be way too powerful, but perhaps due to my inability to use them well, I really don't find wardog "wargods" - perhaps only refers to the divine ability of full regeneration after every battle?

Also, I wonder whether the "fear factor" can accumulate if we have mulitple units of dogs charging the same target...? But if they rout, the dogs will chase them all the way out of the field, which is also a big waste.