I was sharing a house with a few other people and the exhaust fan over the kitchen stove got a lot of use. I didn't use it myself. Just opening the window cleared out the smoke, flames or whatever faster.
I couldn't see an exhaust vent on the outside wall of the house near the stove, so I asked the landlord out of curiosity where the exhaust went. He said it went up the internal wall to the attic, then across to the soffit at the bottom of the roof and vented there.
I checked the attic and it did not. There was no duct for it at all.
The fan just blew the bacon grease into the wall. There was no exit for it.
Whoever installed the range hood had skipped the hard work part. It would have been difficult to run the duct through the wall into the attic. It had been done years before and the landlord had never noticed, but it wasn't pleasant for him to find out.
So basically the fan was doing more harm than good. The wall was probably loaded with moisture and mold.
Have you ever been affected by this sort of 'workmanship'?