What type of process ?

Is it GTAW in AC mode ?
In that case the arc balance adjusts the penetration in aluminium welding :

(1) no balance = 50% electrode negative and 50% electrode positive
(2) with balance = you can increase/decrease on a relative time scale the period of electrode positive/negative (0-100%)

* increasing electrode negative
(=automatically decreasing electrode positive)
this will increase penetration

* increasing electrode positive
(= automatically decreasing electrode negative)
this will improve the breaking of the oxide layer (with high melting point)

That's balance control on an AC Tig welder !