What is "break in" and what difference does it make? In amps? Preamps? Speakers? More?

Just about everything breaks or runs in. Cars clothes shoes and yes even electronics. Speakers like shoes are stiff when new and soften up with use and become more flexible and thus sound smoother etc. When designers are voicing speakers they usually do so with fully broken in drivers so they sound as intended when broken in not when new and stiff. Electronics have there own version of this.

This question has been asked and answered 71 times already.

Sorry to ask a question that’s been asked so many times. If it were possible, I’d just delete this question and try to come up with something more novel. But I suppose people can just skip answering it. Or give 

You’ll get as many opinions as comments on this, my personal experience is most break in is between the ears, you get accustomed to the sound. President and designer of a speaker company told me that would be the case with his speakers as they are played for a couple of hours before shipping so I wouldn’t notice any mechanical changes. My opinion is it might take a few seconds to perhaps an hour for all the electronics in a component to " break in" of course it takes tubes a while to heat up but other than that I never think of or worry about break in but some say they can hear a fuse or a mains cable break in, I never have.

+1 djones51!