I think that lipo pack is a standard rc type pack with a balance lead. (from memory, without looking it up)
So, yeah, B+ and B- are to charge. The balance lead is to hook up to a proper balance charger to get all 3 cells to a full 4.2v when charging. Instead of one @ 4.15, another @ 4.20 and the other at 4.25 volts.
I'm 99.99999% sure that mod is charging to a total voltage, not a per cell voltage since that balance lead is not hooked into anything so there is no way for it to know individual cell levels or pull power from the high cell(s).
If you don't take the charge down to too low of a level it's probably ok to balance every few days as the cells levels shouldn't wander too much but over time they will and the danger is that when charging you could be taking one cell over 4.2v and on the other side if you run it all the way down the weakest cell may be dipping down below what you would want as the lowest.
Most likely the damage to a pack in this application is over charging, I doubt people take their mods to cut off voltage often but they do fully charge just about every time.
The good thing is that you can get packs for probably about $5 from hobbyking that still have 4 times the discharge rate a mod needs. So who cares if you shorten the life of the packs because you dont balance charge at that price. You should still see long life (6mo?) and ease of use.
What a pain in the ass it would be to drag the power supply and balance charger out every time you wanted to charge lol.
If I owned a mod like that, I would probably balance once a week and call it good.