Originally Posted by fq06

Some don't balance charge but the tech in the good chargers now makes it to where it really doesn't take much longer and it is safer for your packs.

If one pack is 0.3v lower than the other and you non balance charge, charger will stop when it sees a full 8.4v. But one pack could be 4.0 and the other 4.4.
Not good, over charged cell.
Then when you run the lower cell may get lower than you would want because the esc is just looking for an overall 6.8v (or whatever you set it at, I use 7v) to cut off at.

Anyway, short answer, it's best to balance charge to make sure both cells are at the same voltage.