Avoiding using the car's defrost mode for extended periods is important to reduce fuel consumption and prevent damage to your car's engine. Defrost mode is a feature in most cars that uses the car's air conditioning system to remove moisture from the air and clear the windows of fog or frost.

However, using the defrost mode for extended periods can cause the car's engine to work harder and consume more fuel. This is because the defrost mode uses the car's air conditioning system, which requires energy to operate. The more you use the defrost mode, the more energy your car's engine has to produce, which results in higher fuel consumption.

In addition, using the defrost mode for extended periods can also cause damage to your car's engine and other components. This is because the defrost mode puts extra strain on the car's alternator, which is responsible for supplying power to the car's electrical system. Over time, this can cause the alternator to wear out faster and lead to costly repairs.

To avoid using the defrost mode for extended periods, try to clear the windows manually using a scraper or by opening the windows slightly to let the moisture escape. You can also use the car's air conditioning system in combination with the heater to clear the windows more quickly and efficiently.