Very good question.
I have recently noticed my Shark 4-way OFC cable
showing these oxidised signs along the cable, which in my view must be a bad thing since at 620 strands of 0.07 on each core, each strand relies on contact to the next by wound surface contact to make up the bundle. Also I thought higher frequencies concentrated themselves near the surface of these smaller strands while the 'juicy' part of the signal needed the thickness.
Fortunately, I'm re-introducing 7 singular power amp modules, each with their own toroidial transformer placed at the bottom of each floorstander/centre/surround so will have a tiny amount of speaker cable to travel. Instead I will have a singular HQ OFC coaxial to each amp, but then the same thing applies to that but it's much cheaper to replace.
Cable like my Van den hull etc hasn't oxidised etc being plated. Some like Van Damme speaker cable I have when you strip the jacket at the termination point again it's still 'sweet' and fresh.
I think this goes to show how well made some cables really are. I think my Shark 4way is rather poor to be honest. Mind, I didn't pay what it costs now & it's quite old now.