Leaders have massive impact to the combat ability of units. (Like you can easily double the combat value). There are leadership's check everywhere in combat and during logistic phase.
The closer the leader is to the unit, the most impact he have. If a check is failed at army level, there is a try at front level, then at stavka level, with increase difficulty each time.
Relative to success chance, (using perfect distance to the unit and no overloading and no additional factors), the chance of success of a leader check in an attribute of value 5 is :
50% at army level.
25% at front level.
12.5% at Stavka level.
So Zhukov can be a godlike leader providing insane boost for a small number of unit at army level, a very good leader providing good boost for 4 time more units at front level, or a good leader providing small boost at stavka leader for all your units.
What you prefer is your personnel choice.
PS : Alternative CV calculation take leadership into account for CV display, you can use this option to have a feedback of average leader effect.
PS : Distance to unit and especially HQ Overloading KILL the benefits of having a good leader.
Thanks, that was really useful. A couple of questions:
Does this apply to all leader attributes? So, Zhukov at STAVKA would use his Infantry rating to give a 12.5 percent chance of every infantry unit passing a combat check?
Is the bonus all or nothing? Does, say, assigning Zhukov to command an army versus commanding Stavka just affect the probability that a unit under his command will pass a check? Or is there an actual bonus that depends on what level of command Zhukov has been assigned to?