Originally Posted by
NA12ChupaCabra
Leadership is used to determine how big of an army your hero can effectively lead in battle. If your army is bigger than that, your hero will get a penalty.
The popular belief is that you can use the following formula to determine this:
Max Troops = (LD * 10) * (LD + bonus)
Where LD = Leadership attribute. Bonus is based on the minimum star level and the value is 14 for levels 5-8, 20 for 9-11, 25 for 12-13, 28 for 14, and 32 for 15. ** numbers may differ a little.
It's believed that the penalty is applied to the heroes attack rating for offense and intel rating for defense and it's value is the percent over maximum troops. ie: If you are leading and army 10% over the max, those two attributes will drop by 10%.
It gets a bit tricky when determining this as it also seems to include stack size. If two stacks are under this size individually but over it combined, the penalty is applied to only one of the stacks. The stacks are checked/penalized in a specific order.
Unless you are trying to write a combat calculator yourself, you really don't need to know that info. A good estimator is that your hero can lead 1000 * LD effectively (ie: a 100k scout bomb with a lvl 100 hero is optimal wheres a 100k bomb with a lvl 40 hero is not).
I'm too lazy to find the posts about this, but checking Un3x's posts you will find them.