Anno v. Heimburg writes:

NB that I'm not saying that this position is necessarily marked anywhere,
nor that it is relevant to actually flying the plane.

It is slightly relevant. If you have a substantial amount of trim set
for a control surface, the distance remaining to the limits of its
travel are substantially modified, and you may forget about the trim
and mistakenly believe that you have more remaining control authority
than actually exists.

Also, if you have trim set but you think it's neutral, you may be be
actively compensating for changes induced by the trim. In some
aircraft, you can see the position of the controls and deduce that
some trim must be in effect, but in other aircraft you cannot.

Both of these potential problems can be avoided by keeping a strong
awareness of the trim state of the aircraft. As long as you keep in
mind that you've applied x trim while flying, you should be fine.

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