"Choreboy" wrote
I was amazed to discover only wood under the shingles of my house, which
was redone about fifteen years ago.

A neighbor said several roofers have told him that's the best way to do
it, and he intends to nail his shingles directly to his planks in the
future. Roofers have told him roofing felt shortens the life of
shingles by causing them to get hotter in the day.

I don't believe the felt makes shingles hotter, but I wonder about
moisture. Is it possible that in some circumstances, the layer of felt
can make shingles more hospital to fungi?

Has anyone else heard the theory that it's better to skip the felt?

It's not a theory, it's a short cut commonly used by hacks.