It goes without saying that a bathroom fan that just vents straight
into the attic is a house destroyer. Run solid duct to the outside
(and insulate to avoid condensation).

The bathroom vent on a timer is not to alleviate moisture problems,
it's to ventilate your house (the envelope, not the attic). This is
an alternative to just letting the air leak out through the attic
which (a) let's warm moist air into the attic (b) let's your energy
leak out. You really only need to ventilate in spring and fall (too
cool to open windows, but your furnace isn't dragging fresh air in).

Fix the air leaks from envelope to attic, and you may not even need to
ventilate the attic. Then ventilate the house envelope itself in a
planned and controlled fashion. Soffit and ridge vents have nothing
whatsoever to do with ventilating the envelope.

A dinky little bathroom fan is not going to create low pressure in the
house, I was not talking about an attic fan which is overkill for this
purpose. Your furnace already pulls air into the house through
windows etc.

Having said that, it is important to do this as part of a whole-house
air-sealing business, so you know where your fresh air is coming from.
Ex: most houses drag in air through the crawlspace, not a very
healthy zone. You should be air-sealing anyway as part of energy
conservation.

See "Insulate and Weatherize" by Bruce Hartey for more information.