Over 25 years, I gutted my basement twice before learning this lesson. Exhausting basement air draws outside air into the home. This is OK when the outside dew point is less than 50^F. When the outdoor dew point is +60^F, basement ventilation causes condensation on the concrete. This like the condensation on a can of cold pop. Damp concrete grows mold. Mold makes a basement smell like a basement. Damp, musty basements make people sick. Get a % relative humidify meter and monitor the %RH. When it's exceeds 60% RH, stop outside air infiltration and dehumidify. To be realy safe, you should keep the humidity below 50%RH. Even climates like Denver that are dry most of the time have this problem after a week of rainy weather. A dry basement space is the nicest space in a home!