bob haller wrote:

in the summer with AC sucking cooled air from the air conditioned
space is a poor choice, but at the same time its when having a
cool attic is most important....

beyond which sucking on the living part of the home will create
paths for the air from the living area to follow all the time...

In the summer, if I had a choice between:

a) pulling 1000 cfm of air out of my attic using powered vents - with
950 cfm coming from the soffits (and/or gable-end vents) and 50 cfm
coming from ceiling leaks - or

b) having NO powered vents (only passive vents) and therefore only
getting 200 cfm of passive air movement out of the attic (and 0 cfm from
ceiling air leaks) -

It's a no -brainer which one is better for the house and the roof.

And if I can pull more than 50 cfm from ceiling leaks, then the answer
is NOT to turn off the fans. The answer is to fix the ceiling leaks (or
just live with them) - not sacrifice the life of the shingles by letting
attic temperatures soar.

roof fans in the winter help keep the humidity low in the
attic which helps prevent mold growth

I would bet that the vast majority of roof fans don't have humidity
sensors - only thermostats (which means they only come on in the
summer).

I know the theory of ventilating the attic in the winter to prevent
mold, but explain to me how discharging cold, humid air from the attic
and replacing it with cold, humid air from the outside is going to
change anything.

If the air in the attic is more humid than outside air in the winter,
it's because you have ceiling air leaks (or you're venting bathroom and
kitchen exhaust fans directly into the attic). It's a no-brainer that
you fix those situations first, eliminating the need for winter attic
ventilation in the first place.