After a certain time, you will gain a random trait that makes you gain bonuses. The leader does anyways. If you switch leaders, you can let everyone get a chance to find their own special ability.
Here are some for starters.
-Increase Gold Drop
-Extra Damage
-More Accuracy
-More Chance Of Recruiting CPUs
-Weather Related Bonuses
-Air Strike At One Time
-Invincibility For A certain Time
-Repair Over Time
-More Range
-Piercing Damage
The list can be upgraded and there are variations. Couple these with masteries and switch out leaders for a good teamwork battle strategy.