[Si Coe]

From the plane guys, who have been using Lipos way longer than us:

Balance charging is not essential, but it is a good idea. If you don't run the pack all the way down to the LVC (which you wouldn't in a 5 minute race) there is very little risk of a cell going under 3V. It could have a slight effect on performance if the two cells are significanly out of balance, and that would in turn cause a shortened lifespan.
It is certainly advisable to balance when possible but with careful use dozens of charges can be safely performed without balancing.