I am a believer in break-in of audio components. I realize that some disagree, and I am open-minded enough to accept their right to be wrong.
Once I hooked up a system with a long run of cheap speaker wire and the sound was way too harsh. I did a seven-day break-in with a cable burner and was rewarded with acceptable sound. I have a Cable Cooker and have always “cooked” my cables three days just on general principles, though I should report that my cable suppliers do not think the difference is large.
Some say that when you break in speakers you are deceiving yourself that they sound better after break in because you are just getting accustomed to the sound. Not so. When I had a storefront I often put new models of small speakers on display, only to hear weak bass and harsh highs, so I made it a practice to break them in by putting them in a storeroom hooked to the low voltage tap of a transformer. Two or three days of continuous 60 Hz was enough to significantly improve the sound..
Listening only before and after break-in meant that I had not grown accustomed to the sound, and in the store I had the added advantage of daily comparing various speakers with a switcher with our very familiar playlist of demo tracks, so I knew the sound of each demo track and each speaker from excessive repetition. (Yes, I have heard Dark Side of the Moon more than once.)
With electronics , because I lack confidence in my memory and because it takes at least a week from first listen to the broken-in product I don’t even try to compare before and after sound. I do, however, have several friends whose hearing and memory I trust. I believe them when they tell me the improvements they hear make as much as 15% to 20% improvement.