It's very standard for both the general public and professionals... there's nothing esoteric about it... it's very inexpensive*... and helps to break ground loops, etc.
Reasonably, you could use just one source or receiver side, but if in doubt, it's better to have two... they had a bad reputation in the 90s because they were poorly made, but now they're very efficient...
You'll see them everywhere... but not in our Wiims yet (and if you don't see one in your DACs or digital source connected to your Wiim..all the more reason to have one in there ;-) )
My comment may seem negative to you... but the fact is that it's mainly Wiim's "oversight"... that's all... I'm pointing it out hoping that Wiim will address it in the future...
;-)
( * ex da101c murata...same from pulse etc)
Small black cubes, easy to spot near your digital inputs and outputs... ;-)