I recently came across a YouTube video where a guy rewound a microwave
transformer to make a spot welder.

In talking about it, he stated -- and repeated -- that it was very
important for the secondary winding to have the same "sense" as the
primary -- that is, both windings had to go around the core in the same
direction.

I know that matters if the transformer is handling very asymmetric
waveforms such as in a flyback configuration, but I have never heard
that it matters for plain old 60 Hz. sinusoids.

Does it? Or was the guy just confused?

Isaac