Balancing is becoming more the norm, look at the manufacturers now offering charge jacks for that very purpose. On a 3cell pack the center cell cannot dissipate heat as efficiently as the outer packs which can be a factor in the cells getting out of balance. Once out of balance the charger will overcharge some cells while it is trying to bring the whole pack up to where it thinks it should be. Without being able to charge the cells individually you have no idea what shape your packs are in and can easily shorten their useful life span.

Balancing is simply the act of charging the cells individually as opposed to charging the whole pack.