Audio summing mixer- inverting or non inverting output?
When listening to a single channel, delay or inversion doesn't matter.  When the overall audio has multiple signals (stereo has two, for example), then the relative phase or inversion between channels matters.  You can invert all channels or none.  Inverting some but not others messes up the phase relationship between the channels and the sound position you are supposed to perceive from them won't be correct.