Many homes I encounter as a St Louis home inspector have had the bathroom exhaust vents added since originally being built, have added bathrooms, dryer vents, or the current Buyer would like them added.
Exhaust vents are an outstanding way to prevent the moisture from bathroom activity from permeating into the walls ceiling and structure of the home, and the items in the room. A dryer vent does essentially the same thing. Removes air with a high moisture content from the home.
Sometimes I find exhaust vents wired to the same circuit as the light, which can dim the light when the exhaust vent is turned on. Sometimes they are wired from a GFCI protected receptacle, which can cause unnecessary tripping of the device, among other things.
What I find often, though, is that these vents are not properly vented to the outside of the home. Sometimes a crawlspace, or a garage, and most often into the attic, all of which only relocate the moisture issue.
There are, of course, specific roof boots and wall vents for this very purpose. They are, admittedly, more difficult to install in a finished home than when the home was being built. But it can be done.