I suspect people get something out of taking things apart. IN doing that,
they make the piece of equipment less of a black box, and putting their
hands on it when they can't hurt it (because they've decided it's junk
already) takes away some of the fear.
Tracing the circuit is another way. There is fear of not knowing what's
there, there is fear of some mystery circuit. Yet tracing the circuit
gives you intimate contact with the unit. It's something as valuable
as just taking junk apart, in devaluing the mystery.
And as he said, it's likely to be pretty standard. And that's one of
the tricks of circuit tracing. Get a bit of information, and then make
the assumption that it's a fairly standard circuit based on that information.
So if it uses a certain IC, you look at the manufacturer's datasheet or
application note for the device, and then use the "suggested circuit" and
see if the unit's circuit matches that.
The beginner will always approach things in the "it must be a mystery, I
need a schematic". But, it's not always beyond them, it's merely that
they perceive a big first step. But the "oldtimer" who is capable in
such things, they likely got capable because they got over that perceived
need for a schematic, and they started signal tracing and making assumptions
that the circuit will be fairly standard. Hence the move to an "oldtimer" can
be shortened by making that step early.