Invert ?

Chesky has a test CD with sample jazz tracks from their catalogue.  One of the teat track offers two pieces of music where a track is played in normal polarity and then in inverted polarity.  With such side-by-side tracks you can see for yourself if polarity matters.

Speaker design plays a big role in whether polarity is heard.  Designs that attempt to preserve phase relationship and timing of arrivals of sound from each driver will make polarity more obvious.  If you cannot hear polarity change because your speakers muck up phase/timing relationships, fear not, many very good speakers are not good at this test.

Phase inversion drives me crazy.  I own a lot of Conrad Johnson equipment.  

Some components phase invert, others don't.  

I've recently installed a Schiit phono stage.  I asked their online AI, and get a 'maybe yes or no'...so much for AI.  No reply from a human as of yet...  It makes a difference! 

Your switch gives you one phase inversion, if you wish to use it!

If anyone determines their absolute phase (total system) is not of the correct polarity, and have no switching to use in the system, simply reverse the leads on the speaker cables at the speakers. 

Thanks everyone for all these great explanations. One question   How do u know if a recording is out of phase? How often does this happen in a recording? What is the best way to tell ? 🤷‍♂️

@OP, there's no way to tell except by listening. MWH777's post explains it well. To the extent that it is audible, the effect is likely to be more obvious by playing some simply mic'd recordings .