Questions about the gameplay of Heroes 6.

I wouldn't take it. It will instantly eliminate all those distracting units and similar things. Sometimes it's beneficial to leave a couple of barely alive archers on the enemy side, who won't cause much damage, but will give you a good opportunity to heal your units. Just make sure to skip a few turns. And then BAM! They are killed by your siege master. The battle is over, and the corpses remain...
No, it's better to play in a way that allows you to control the situation.