[BrianG]

Balancing ensures that each cell in a lipo pack has the same exact voltage. A charger by itself will put out max of 4.2v times the number of cells. However, the charger doesn't know if one cell is higher and another cell is lower.

For example, when charging a 4s pack, the charger will put out a max voltage of 16.8v. If one cell is higher for whatever reason, say 4.5v, the other three cells could be at 4.1v and the charger would never know. A balancer would insure that 16.8v is divided perfectly equally among each cell for 4.2v each.

Higher quality packs like those might be matched so an imbalance is minimal, but it can happen, particularly if you exceed the discharge C rating, or drain them a bit too far.

In short, always balance. It may be unnecessary, but I would rather play it safe than sorry. Just my $0.02.