Let it be YES, Please!
There are so many situations where I don't want the idiots involved in the war. I even find myself wasting units to give them someone to attach to, so I can escort them safely to an area where they can do no harm.
Please, please, let me be able to tell them to stay home.
I hate my low tech groups vassals when it comes to show superiority war goal as much as I love the ennemie's!