Foggy windows can reduce visibility while driving. If moisture is collecting on the inside of your windshield, the defroster can help clear it by directing air toward the glass.
One mistake to avoid is leaving the climate control system in recirculation mode while trying to clear interior fog. Recirculation keeps cabin air circulating rather than bringing in outside air, which can allow window fogging to continue under certain conditions.
For interior fog, use the windshield defroster with warm air and an appropriate fan speed. Select fresh air rather than recirculation, and use the A/C dehumidifying function where recommended by your vehicle's owner's manual.