I think that the point is, if you are growing in a 'soil' medium, is that chlorine does not discriminate which types of bacteria to kill.
Meaning that if you do not take measures to remove or lessen chlorine levels in your water you could be killing the beneficial microbeasties in your medium which help your plant thrive.
You might believe its worth killing off all the bacteria as you will be killing the bad ones too, but I think that is it generally believed that the good bacterias kill off the bad ones anyhow.
So as potable chlorinated water is not necessarily harmful to plants, you may hindering its growth by killing off the beneficial microbes present in your medium.