Bee is talking about the balance of positive to negative chakra required to make the technique work. I haven't read this chapter or seen the corresponding episode in a while now, so I might be off about the fact that it is only for this technique that the balance matters, but I seem to recall that it is specific to the TBB/Tailed-beast Rasengan. See, a tailed beast's chakra is made up of positive black (or blue in the anime, if I recall right) and negative white (red in the anime) chakra. There needs to be 8 units of one for every two units of the other for the balance to be perfect!