Also 'wear' would not explain why a unit is alleged to require a fresh
warm
up for each new use after it has been left unused/unpowered for some
time. Hence my understanding is that people are not describing 'wear',
but a change that undoes itself with lack of use and has to be redone
when use recommences.

Such as when components selected in the design (for whatever reason) are
such as to perform at their optimum when they increase in temperature?

The difficulty with such an approach is that the designer has to make even
more assumptions than usual about the user's conditions of use. Thus on a
hot day, or in a cold house, the unit may simply never settle into the
'intended' operating conditions. This may mean more that a slight change
in
sound quality.

FWIW when developing I often used to shove an amp into the fridge
overnight. This gave a few mins in the morning to see what it did when
cold. This swiftly showed me that quite a few designs did *not* like this,
and proceeded to be more prone to things like bursts of spurious
oscillation. Took time and effort to design out problems like this and get
a unit that would work at almost any 'room temperature' any sane user
could
be expected to have!

I'm curious: did you always achieve the exact performance you were after, or
did designing out one problem lead to compromises in other areas? I would
imagine that designing commercial product requires all sorts of compromises
anyway, but were there times when the trade off would be too great?

Hence my personal view is that the designer should be dealing with this.
Not making assumptions about the user always being in a given room
temperature, and air-flow around the unit.

Even if the designer felt that the "typical" performance was superior (or
simply more popular and therefore more profitable for his company)?

Slainte,

Jim