To Flame or not?

In the demo, your can light the arrows of your archers.
I would like to know what advantage-disadvatage it has, or for what purpose it serves?

like advantage-, flame arrow more morale dmg.?
disadvantage - lower rate of fire, lower volume of arrows on target?

thnx for clearing this up.



About field fortifications, like in agincourt (and the other map). Is it possible to do this in the full game? like when a army in on the defence (standing still that turn) and can make ditches, traps, pikes etc.