I don't think that it is useless, it can be really good. Especially in tight land, where the enemy has no other choice then to cross it to get to you. Over there, you can use it even better, because they have to walk longer over it.
At first, youre archers can shoot one or two more arrows at him, if he then looses the battle or your support troops arrive and he has to retreat, you run after him and you are able to kill even more of his troops.
Because of that it is of course much more useful in pvp online games than against AI.