Quote Originally Posted by Morindin
At first I used fire arrows because they looked so damn cool.

Now I rarely use them against anything save enemy siege weapons, normal arrows can rout lightly armoured or slow moving units before they reach your line by inflicting mass casualties quicker than fire arrows will.
Those are the things I use the fire arrows for as well - but I do also use them at the end of battles as they tend to make tired/exhausted soldiers rout easier.