Cable burn in does work! Now, what does work, is that the more effort you put into a possession, the more you will enjoy it (cognitive dissonance theory). Burning in cables for the recommended 200 hours is a PITA. Placebo. Which, mind you, is real, and contributes to happiness. So, IMHO, it's not such a bad thing. Also, I've worked in electrical and chemical research engineering, therefore, I'm qualified in informing you that if you put too much current through a cable, you get that nice blue smoke.
But in all seriousness, it's funny, and kind of sad to see people selling and buying this snake oil. That people are making a profit from this is infuriating. But it creates economic liquidity, which helps the economy. So it's not that bad, if you think about the big picture.
Cable burn in, in the audio amounts of current and temperatures, is total, utter, rubbish. It's the same thing for cryogenic cable treatment. The only thing you are going to do is cause differing contractions and their subsequent expansions with the differing materials, and then you are just potentially causing stress fractures. Nobody is saying that that is any good.
When a (normal) material is already solid, stationary, and not subjected to ridiculous outside forces (extreme ionizing radiation, neutron star levels of magnetic or gravitational tidal forces, telekenesis, etc), you won't change crystal boundaries or any such thing by cryogenically freezing it to liquid nitrogen levels. Not something as stable as copper. I can't say the same for exotic materials, liquid crystals, dark matter, unobtanium, or cooling to less than 4 kelvin (weird stuff happens there) as I'm not familiar with them, but you get my point.
Burn in of moving parts, yes, that is very real for many reasons. But that's not what our concerns are here.