Funny, I watched "Ask this Old House" Thursday night. A homeowner had
an exhaust fan installed in their bathroom. The electrician claimed it
was unnecessary to vent it to the outside, so he just installed the fan
so it vented into the attic.

The homeowners ended up having water damage to their bedroom ceilings.
It was winter when they went into the attic to see if they could find
the problem, and they found sheets of ice on the inside of their roof.