Depends on the home. My parents house wasn't designed with one. My house is designed with one. It took me about a month to understand that it acted like a giant leak in the house. When the wind blows across the exhaust it pulls air in or out. Also, it allows rodents and insects to come in & out as they please. So I just plugged the thing up with some old rags.
Another option is an anti-backdraft cowl and some insect mesh... if you have an air quality monitor take a look some time at what happens to the air quality in your kitchen when cooking (especially frying) - it generally takes quite a dive, particularly if you have a gas cooker.
indoor CO2 goes from like 500 ppm to 950 ppm. It's awful. I avoid using the natural gas oven and range when I can. I intend to install an outside air exchanger, but haven't got around to it.
