Burn-in question

The run in or burn in is largely permanent, but most gear does need to take time to stabilize at running temp. There are various reasons for this, some of them speculative - some of them known quantities.

Specifically amplifiers tend to require this, depending on the given design. This is due to bias and crossover stabilization at their ’operating temperatures’.

and resistors...?

If you believe in burn in then there is no logical reason to think that it will ever stop - so might as well call it drift or premature aging or poor temperature stability or early electrical break down. (Unlike mechanical vehicles with friction on moving parts where it can be assumed that break-in will occur over the first 1000 miles and then a period of good stability is to be expected => there are no moving parts in audio electronics)

Certain types of Caps and especially electrolytic ones do break down over time but I would call this aging as the period of stability is early in the use of the device before heat and extended use cause it to break down.

Speakers that are poorly designed may require break-in. (Poor design means that mechanical friction of spider and surround is very large compared to a very weak drive motor. Woofers lacking air suspension or a speaker box would be more susceptible to break in)

The manufacturer and owners of the high end burn in device Cable Cooker by Kafton actually report that re-burning cables in say, once a year is effective, so one might reasonably conclude that yes, burn-in is not permanent. Not to mention the conclusion that playing music through cables is not as effective as more stringent methods.

Bare also in mind that Cable Cooker certainly has direct financial interest in re-burning statement 

That's a stretch. Besides, the Cable Cooker customers have no financial interest in making that observation.  Don't be such a conspiracy theorist.

Just use this Pink Noise Generator (pink button), raise the volume and leave it on while your at work, press the oscillate high button to vary it up and down. forget all the voodoo gimmicks that cost money.
https://simplynoise.com/

Cheers George

@audio4pass, you reopened the proverbial can of worms and you are going to hear from both sides of the spectrum.
With that said, based on my experience and examination: +1 teo_audio.