I love trenches.
Last night destroyed 2 full stacks of enemies losing like 2 or three units...
You have to make them where you expect to be involved in a shooting match; i.e. when the enemy attacks with low melee stat units and you just don't see going to melee as a viable option (they have a lot of cav?). Then the barricades are a life saver.

The best part is that dug-in artillery does not get killed by the enemy sniper artillery