This is strickly from a MP point of view.

You should always be using your crones for some magic beatdown; yes.

But psychology is just as much a part of diplomacy as position and power. And a numbers and scouting (and in turn opponents scouting you) play a large role in when and where you will be attacked.

That is why I consider 2 or 3 Crones on Vine Duty if they are not needed in a desperate fashion, essential to having a quick reinforcement/Call of Wind/of the Wild beatdown force as well as a psychological gauging of numbers by your opponent.