break-in--bane or boon ??

as a reviewer , i often receive equipment which is new and has no playing time.

i have to decide whether to break in the component and if so, how many hours is necessary.

i have often asked manufacturers for guidance.

one cable manufacturer said the cables--digital, analog and power, required no break in. another said 24 hours.

when i reviewed a mcintosh tube preamp, i was told by a technician that no break in was necessary. all i needed to do was leave the preamp on for one hour in order that the tubes were "warmed up"

can someone provide an objective explanation as to the basis for break-in and how to determine how long to break in different components ?

for example, cables comprised of different metals, if they require break in, is there a difference in the requisite time for a given metal, e.g., gold, silver or copper ?

can someone provide an explanation as to what is happening during the break-in process ?

can one devise a mathematical equation to quantify break-in hours, as a function of the parts in a component ?