What they do is separate the good electricity from the bad. A sort of St. Peters Pearly Gates or Santas list, if you will.
If they are too short (now we know), then some of the nasty electricity gets through and invades your precious equipment. This filthiness manifests itself in less than absolutely-positively-unquestionably black backgrounds (when it could be blacker than black, mind you), and countless other aural malaise. So its molto important to have at least 6 or more feet of really, really expensive cable if you are really serious about nabbing all the sinning particles of power.
Once you accept this as your mantra, you will sleep better at night and Ill be able to recommend some excellent psychiatrists. I am fortunate to live in a large northeast US city where there are many understanding doctors who dont mind when I come in for sessions wearing a interconnect for a belt and two beefy PCs for suspenders.
Now, lets talk about vinyl or compact discs...
Rufus