Hi,

What's the point of caulking the roof flashing for the exaust fan
vent?

Specifically, I'm talking about what takes place at 2:20 in the
following video:

http://youtube.com/watch?v=IrwWOW9RE3Q

It seems to be protection against the water flowing up. Is this done
to protect agaist the moisture drawn up by capilary forces? And in
that case, are the shingles themselves caulked?

Thanks!