Most modern bathrooms have a fan in the ceiling to remove excess moisture and unpleasant odours! Back in the 70's and 80's they were often vented into the attic space which turned out to be a bad idea as mold often formed which created a dangerous situation. But we have learned from those mistakes and they are now vented to the great outdoors.
Properly functioning bathroom fans are important as we add a lot of moisture to the air when we shower and if it isn't removed can result in damage to painted walls, mold growth, and even rotting of wood surfaces.
Air movement by bathroom fans is measured as cfm (cubic feet/minute). For a fan to work properly it needs to have enough cfm's for the size of the room. Usually 1 cfm per square foot gives an adequate air exchange. This can be calculated by measuring the room. For example, if your room measures 7ft x 10ft you multiply to get 70. You would then need a 70 cfm fan.
Bathroom fans also come with sound ratings called sones. A 1 sone fan would be very quiet while a 4 sone fan would be louder.
With time, fan grilles and motors can become coated in a fuzzy coating of dust. This can make the fan work harder and wear it out sooner. So it's a good idea to give it a vacuum periodically.
Sometimes older fans become noisy and and may even stop working all together. In that case it may be time to call your local Handyman to determine if it needs to be repaired or replaced.
While not very exciting, bathroom fans are a simple but important part of your home!