Ivaenol

You are going to get mixed feelings about this.
While many forum members say that this communication is mandatory, I have personally never used this feature. I have also seen many installations by other installers without said cables. My personal reasoning is that the BMS takes care of balancing and protection from overcharge or overdischarge. The charge controller only charges to a certain voltage and the inverter switches off at a certain discharge voltage. For me that is good enough. 
 
The one area I could foresee a problem arising is if you had too small a battery bank and too big a solar array. In that case communication might help to keep the charge amperage to acceptable level.