Charges have real power and can completely break lines, so it's important to ensure troops are in a dense formation where they can absorb the inertia, although that makes them a sitting duck for artillery, magic or huge creatures. And by huge, we mean huge. The really big nasties tower over even castle walls and send swathes of soldiers flying into the air with every mammoth swipe.
Then, of course, if one of these behemoths is slain you've got the aforementioned falling down, and it's time to start praying they tumble towards the enemy lines as opposed to your own. Where this mechanic really comes into its own is with flying units - killing something large when it's hovering above your warriors is a mistake you'll only make once.
Above: Armies leave scars - troops destroy grass and trees, leaving a dark rock-filled land
The fantasy setting means there are plenty more interesting tactical options like this. As in Dark Omen and Shadow of the Horned Rat, big, ugly or spooky troops cause fear, and sending such units running at enemies with low morale will most likely make them lose their bottle and flee.