Network Switches

Attended a High End Audiophile event in the weekend here in Copenhagen, where one of the vendors had the AQ SWITCH SE in all his 3 systems (a 15K €, 30K € and 60k € system (speakers, amp, streamer, dac, power plant)). 

I must admit I do not get, if a switch replaces a wifi router or it connects to a wifi router. 

I for one appreciate all the insightful answers and I have no need for people telling me that I my personal experiences are wrong. 

I bought, just for fun, a new Ethernet cable and much to my surprise the difference was clear. I do not understand why it is better, but I do know that it is.