"Its not that important to balance the rear wheel" is a very common misconception.
Balancing the wheel/tyre does 2 things
Reduce vibration which increases grip levels
Reduce tyre wear over the life of the tyre.
An unbalanced wheel/tyre will cause vibration and can effect grip especially on wet/damp surface and the faster you go the worse it gets, the tyre also wears faster as the heavest part of the tyre will wear faster as it tries to bring the Wheel/tyre closer to balance.
Look at the wear on an unbalanced tyre which would require 30 or more grams to balance it, part will be worn completely while the rest will be well within the wear limit.
I have seen tyres worn to 1mm of thread at one point and have 4mm left on the rest.
I have always balanced both front and rear on any bike capable of more than 50 MPH
If you lose more than 5 grams, then you should rebalance the wheel/tyre.
Prior to balancing and changing my own bike tyres I always insisted that front and rear were balanced and any knowledgeable tyre fitter will do it without question.
Many times I had to insist that fitters balance the front and rear wheels/tyres of my car also. The garage I now go to for car tyres, change the valves, balances all wheel/tyres and uses a torque wrench to tighten the nuts on the alloy wheels.