it enables two-head ogre mode
its like archon mode in starcraft
when players in same team controls one peon
u need to set teams in left
in starcraft archon is representing union of 2 templars like 2 players control 1
so in war2 was named two head ogre like 2 heads each is a player in one ogre body 
(but techincally u can even make 7 head ogre
just put 7 players in one team)
ok so after testing around with the new balance mode
my conclusion is this ... i think playing in rebal mode auto heal off is prolly the closest to balance we have
because now that u can select a group of knights an heal 1 knight with out having to have to click alt 1 cntrl 1 it makes healing
way more effective now along with the 1 mana per heal .. so i i could say gow ef rebal no ah meaning no auto heal
and it seems way more balanced with orcs now being able to click 5 knights at once to heal 1 knight in a fight
but with auto heal on i was testing againts computer waiting for orcs to get lust an sending the same amount of knights i had againts there ogres
with auto heal an 1 mana it was way easy for humans to win ... but having to have to heal manually but being able to group knight heal made it alot more balanced